Quinoxaline Derivative, and Light-Emitting Element, Light-Emitting Device, and Electronic Appliance Using the Same

ABSTRACT

A quinoxaline derivative expressed by the general formula (1) is provided. (Each of R 1  to R 12  represents one of a hydrogen atom, a halogen atom, an alkyl group, an alkoxyl group, an acyl group, a dialkyl amino group, a diarylamino group, a substituted or unsubstituted vinyl group, a substituted or unsubstituted aryl group, and a substituted or unsubstituted heterocycle group. Ar 1  represents one of a substituted or unsubstituted biphenyl group and a substituted or unsubstituted terphenyl group, and Ar 2  represents one of a substituted or unsubstituted phenyl group, a substituted or unsubstituted biphenyl group, a substituted or unsubstituted terphenyl group, and a substituted or unsubstituted monocyclic heterocycle group.)

TECHNICAL FIELD

The present invention relates to a quinoxaline derivative, and a lightemitting element, a light emitting device, and an electronic applianceeach of which uses the quinoxaline derivative.

BACKGROUND ART

An organic compound has various material systems compared with aninorganic compound, and has possibility to synthesize a material havingvarious functions depending on the molecular design. Owing to theseadvantages, photo electronics and electronics which use a functionalorganic material have been attracting attention in recent years.

For example, a solar cell, a light emitting element, an organictransistor, and the like can be mentioned as examples of an electronicdevice using an organic compound as a functional organic material. Theseare devices taking advantage of electric properties and opticalproperties of the organic compound. Among them, in particular, a lightemitting element has been making remarkable development.

It is said that light emission mechanism of a light emitting element isas follows: when a voltage is applied between a pair of electrodes whichinterpose a light emitting layer, electrons injected from a cathode andholes injected from an anode are recombined in the light emission centerof the light emitting layer, so as to form a molecular exciton andenergy is released to emit light when the molecular exciton returns to aground state. As excitation states, a singlet excitation state and atriplet excitation state are known, and light emission is considered tobe possible through any of these excitation states.

Such a light emitting element has a lot of problems depending on amaterial in the case where an element property thereof is improved. Inorder to solve the problems, improvement of an element structure,development of a material, and the like are carried out.

As the most basic structure of a light emitting element, the followingstructure is known: a hole transporting layer formed of an organiccompound having a hole transporting property and an electrontransporting light emitting layer formed of an organic compound havingan electron transporting property are stacked to form a thin film ofapproximately 100 nm thick in total, and this thin film is interposedbetween electrodes (see Non-Patent Document 1, for example).

A voltage is applied to the light emitting element described inNon-Patent Document 1, thereby light emission can be obtained fromorganic compounds having a light emitting property and an electrontransporting property.

Further, in the light emitting element described in Non-Patent Document1, functions are separately carried out. That is, a hole transportinglayer transports a hole, whereas an electron transporting layertransports an electron and emits light. However, various interactions(for example, formation of exciplex, and the like) occur on an interfaceof stacked layers. As a result, a change in light emission spectrum or adecline in light emission efficiency may be caused.

In order to improve a change in light emission spectrum or a decline inlight emission efficiency which is caused by the interaction at aninterface, a light emitting element in which functions are furtherseparately carried out is devised. For example, supposed is a lightemitting element having a structure where a light emitting layer issandwiched between a hole transporting layer and an electrontransporting layer (see Non-Patent Document 2, for example).

In such a light emitting element as described in Non-Patent Document 2,a light emitting layer is preferably formed by using a bipolar organiccompound which has an electron transporting property and a holetransporting property so that interaction caused at an interface isfurther suppressed.

However, most organic compounds are monopolar materials having either ahole transporting property or an electron transporting property.

Therefore, a bipolar organic compound having both an electrontransporting property and a hole transporting property has been requiredto be developed.

In Patent Document 1, a bipolar quinoxaline derivative is described.However, since characteristics such as heat resistance are notsufficiently obtained yet, more various bipolar organic compounds havebeen required to be developed.

[Non-Patent Document 1]

-   C. W. Tang et al., Applied Physics Letters, vol. 51, No. 12, 913-915    (1987)

[Non-Patent Document 2]

-   Chihaya Adachi et al., Japanese Journal of Applied Physics, vol. 27,    No. 2, L269-L271 (1988)

[Patent Document 1]

-   PCT International Publication No. 2004/094389

DISCLOSURE OF INVENTION

In view of the aforementioned problems, an object of the invention is toprovide a new bipolar organic compound, in particular, a bipolar organiccompound having excellent heat resistance. Further, another object is toprovide a bipolar organic compound which is electrochemicallystabilized.

Further, another object is to provide a light emitting element and alight emitting device of which a driving voltage and power consumptionare reduced by using the bipolar organic compound of the invention.Furthermore, another object is to provide a light emitting element and alight emitting device which have excellent heat resistance by using thebipolar organic compound of the invention. In addition, another objectis to provide a light emitting element and a light emitting device whichhave a long life by using the bipolar organic compound of the invention.

Still another object is to provide a long-life electronic applianceconsuming low power and having high heat resistance by using the bipolarorganic compound of the invention.

One mode of the invention is a quinoxaline derivative expressed by thefollowing general formula (1).

(in the formula, R¹ to R¹² may be the same or different and eachrepresent any one of a hydrogen atom, a halogen atom, an alkyl group, analkoxyl group, an acyl group, a dialkyl amino group, a diarylaminogroup, a substituted or unsubstituted vinyl group, a substituted orunsubstituted aryl group, and a substituted or unsubstituted heterocyclegroup. R⁹, R¹⁰, and R¹¹ may be combined with R¹⁰, R¹¹, and R¹²respectively to form a condensed ring. Ar¹ represents a substituted orunsubstituted biphenyl group or a substituted or unsubstituted terphenylgroup. Ar² represents a substituted or unsubstituted phenyl group, asubstituted or unsubstituted biphenyl group, a substituted orunsubstituted terphenyl group, or a substituted or unsubstitutedmonocyclic heterocycle group.)

Another mode of the invention is a quinoxaline derivative expressed bythe following general formula (2).

(in the formula, R⁹ to R¹² may be the same or different and eachrepresent any one of a hydrogen atom, a halogen atom, an alkyl group, analkoxyl group, an acyl group, a dialkyl amino group, a diarylaminogroup, a substituted or unsubstituted vinyl group, a substituted orunsubstituted aryl group, and a substituted or unsubstituted heterocyclegroup. R⁹, R¹⁰, and R¹¹ may be combined with R¹⁰, R¹¹, and R¹²respectively to form a condensed ring. Ar¹ represents a substituted orunsubstituted biphenyl group or a substituted or unsubstituted terphenylgroup. Ar² represents a substituted or unsubstituted phenyl group, asubstituted or unsubstituted biphenyl group, a substituted orunsubstituted terphenyl group, or a substituted or unsubstitutedmonocyclic heterocycle group.)

Another mode of the invention is a quinoxaline derivative expressed bythe following general formula (3).

(in the formula, R⁹ to R¹² may be the same or different and eachrepresent any one of a hydrogen atom, a halogen atom, an alkyl group, analkoxyl group, an acyl group, a dialkyl amino group, a diarylaminogroup, a substituted or unsubstituted vinyl group, a substituted orunsubstituted aryl group, and a substituted or unsubstituted heterocyclegroup. R⁹, R¹⁰, and R¹¹ may be combined with R¹⁰, R¹¹, and R¹²respectively to form a condensed ring. A represents a substituentexpressed by the structure formula (4) or the structure formula (5). Ar²represents a substituted or unsubstituted phenyl group, a substituted orunsubstituted biphenyl group, a substituted or unsubstituted terphenylgroup, or a substituted or unsubstituted monocyclic heterocycle group.)

Another mode of the invention is a quinoxaline derivative expressed bythe following general formula (6).

(in the formula, R⁹ to R¹² may be the same or different and eachrepresent any one of a hydrogen atom, a halogen atom, an alkyl group, analkoxyl group, an acyl group, a dialkyl amino group, a diarylaminogroup, a substituted or unsubstituted vinyl group, a substituted orunsubstituted aryl group, and a substituted or unsubstituted heterocyclegroup. R⁹, R¹⁰, and R¹¹ may be combined with R¹⁰, R¹¹, and R¹²respectively to form a condensed ring. A represents a substituentexpressed by the structure formula (7) or the structure formula (8). Brepresents a hydrogen atom or a substituent expressed by the structureformula (7) or the structure formula (8).)

Another mode of the invention is a quinoxaline derivative expressed bythe following general formula (9).

(in the formula, A represents a substituent expressed by the structureformula (10) or the structure formula (11), and B represents a hydrogenatom or a substituent expressed by the structure formula (10) or thestructure formula (11).)

Another mode of the invention is a quinoxaline derivative expressed bythe following structure formula (14).

Another mode of the invention is a quinoxaline derivative expressed bythe following structure formula (39).

Another mode of the invention is a light emitting element using theaforementioned quinoxaline derivative; specifically, a light emittingelement having the aforementioned quinoxaline derivative between a pairof electrodes.

Another mode of the invention is a light emitting element having a lightemitting layer between a pair of electrodes, and the light emittinglayer has the aforementioned quinoxaline derivative.

Another mode of the invention is a light emitting element having a lightemitting layer between a pair of electrodes, and the light emittinglayer has the aforementioned quinoxaline derivative and a fluorescentsubstance.

Another mode of the invention is a light emitting element having a lightemitting layer between a pair of electrodes, and the light emittinglayer has the quinoxaline derivative and a phosphorescent substance.

In the aforementioned structure, the phosphorescent substance ispreferably an organometallic complex including a structure expressed bythe general formula (101).

(in the formula, R¹ to R⁵ each represent any one of hydrogen, a halogenelement, an acyl group, an alkyl group, an alkoxyl group, an aryl group,a cyano group, and a heterocycle group. Ar represents an aryl group or aheterocycle group. M represents an element which belongs to Group 9 orGroup 10.)

Further, the phosphorescent substance is preferably an organometalliccomplex expressed by the general formula (104).

(in the formula, R¹ to R⁵ each represent any one of hydrogen, a halogenelement, an acyl group, an alkyl group, an alkoxyl group, an aryl group,a cyano group, and a heterocycle group. Ar represents an aryl group or aheterocycle group. M represents an element which belongs to Group 9 orGroup 10. When M is a Group 9 element, n=2 is satisfied, whereas when Mis a Group 10 element, n=1 is satisfied. L represents any one of amonoanionic ligand having a beta-diketone structure, a monoanionicbidentate chelate ligand having a carboxyl group, and a monoanionicbidentate chelate ligand having a phenol hydroxyl group.)

Specifically, the phosphorescent substance is preferably anorganometallic complex expressed by the general formula (105).

(in the formula, R¹¹ represents any one of alkyl groups having 1 to 4carbon atoms. R¹² to R¹⁵ each represent any one of hydrogen, a halogenelement, an acyl group, an alkyl group, an alkoxyl group, an aryl group,a cyano group, and a heterocycle group. Further, R¹⁶ to R¹⁹ eachrepresent any one of hydrogen, an acyl group, an alkyl group, an alkoxylgroup, an aryl group, a heterocycle group, and an electron-withdrawingsubstituent. M represents an element which belongs to Group 9 or Group10. When M is a Group 9 element, n=2 is satisfied, whereas when M is aGroup 10 element, n=1 is satisfied. L represents any one of amonoanionic ligand having a beta-diketone structure, a monoanionicbidentate chelate ligand having a carboxyl group, and a monoanionicbidentate chelate ligand having a phenol hydroxyl group.)

Further, specifically, the phosphorescent substance is preferably anorganometallic complex expressed by the general formula (106).

(in the formula, R²² to R³⁴ each represent any one of hydrogen, ahalogen element, an acyl group, an alkyl group, an alkoxyl group, anaryl group, a cyano group, a heterocycle group, and anelectron-withdrawing substituent. M represents an element which belongsto Group 9 or Group 10. When M is a Group 9 element, n=2 is satisfied,whereas when M is a Group 10 element, n=1 is satisfied. L represents anyone of a monoanionic ligand having a beta-diketone structure, amonoanionic bidentate chelate ligand having a carboxyl group, and amonoanionic bidentate chelate ligand having a phenol hydroxyl group.)

Further, it is preferable that in the aforementioned structure, a lightemission spectrum of the phosphorescent substance have a peak at 560 nmto 700 nm.

The light emitting device of the invention has: a light emitting elementin which a layer containing a light emitting substance is providedbetween a pair of electrodes and the layer containing a light emittingsubstance has the aforementioned quinoxaline derivative; and a controlmeans for controlling light emission of the light emitting element. Itis to be noted that a light emitting device in this specification refersto an image displaying device or a light source (including a lightingsystem). In addition, a light emitting device also refers to a module inwhich a connector such as an FPC (Flexible Printed Circuit), a TAB (TapeAutomated Bonding) tape, or a TCP (Tape Carrier Package) is attached toa panel, a module in which a printed wiring board is mounted on the tipof a TAB tape or a TCP, or a module in which an IC (integrated circuit)is directly mounted on a light emitting element by COG (Chip On Glass).

Further, an electronic appliance using the light emitting element of theinvention for a display portion is in the category of the invention.Therefore, the electronic appliance of the invention has a displayportion provided with the light emitting element and the control meansfor controlling light emission of the light emitting element.

The quinoxaline derivative of the invention is bipolar and excellent inboth an electron transporting property and a hole transporting property.Further, the quinoxaline derivative of the invention has a high glasstransition point and excellent heat resistance. Furthermore, thequinoxaline derivative of the invention is stabilized with respect toelectrochemical oxidation or reduction.

By using the quinoxaline derivative of the invention, which is bipolar,a light emitting element and a light emitting device which require a lowdriving voltage and consume low power can be obtained.

Further, by using the quinoxaline derivative of the invention, which hasa high glass transition point, a light emitting element and a lightemitting device which have high heat resistance can be obtained.

Further, by using the quinoxaline derivative of the invention, which isstabilized with respect to electrochemical oxidation or reduction, alight emitting element and a light emitting device which have a longlife can be obtained.

Further, by using the quinoxaline derivative of the invention, along-life electronic appliance which consumes low power and has highheat resistance can be obtained.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1C are views each showing a light emitting element of theinvention.

FIG. 2 is a view showing a light emitting element of the invention.

FIGS. 3A and 3B are views each showing a light emitting device of theinvention.

FIG. 4 is a view showing a light emitting device of the invention.

FIGS. 5A to 5D are views each showing an electronic appliance of theinvention.

FIG. 6 is a view showing an electronic appliance of the invention.

FIG. 7 is a cross sectional view of an organic semiconductor element ofthe invention.

FIGS. 8A and 8B show ¹H NMR charts of2,3-bis{4-[N-(4-bipheniryl)-N-phenylamino]phenyl}quinoxaline, which is aquinoxaline derivative of the invention.

FIG. 9 is a graph showing an absorption spectrum of2,3-bis{4-[N-(4-bipheniryl)-N-phenylamino]phenyl}quinoxaline in atoluene solution, which is a quinoxaline derivative of the invention.

FIG. 10 is a graph showing an absorption spectrum of a thin film of2,3-bis{4-[N-(4-bipheniryl)-N-phenylamino]phenyl}quinoxaline, which is aquinoxaline derivative of the invention.

FIG. 11 is a graph showing an excitation spectrum and a light emissionspectrum of 2,3-bis{4-[N-(4-bipheniryl)-N-phenylamino]phenyl}quinoxalinein a toluene solution, which is a quinoxaline derivative of theinvention.

FIG. 12 is a graph showing a light emission spectrum of a thin film of2,3-bis{4-[N-(4-bipheniryl)-N-phenylamino]phenyl}quinoxaline, which is aquinoxaline derivative of the invention.

FIG. 13 is a graph showing an oxidation reaction characteristic of2,3-bis{4-[N-(4-bipheniryl)-N-phenylamino]phenyl}quinoxaline, which is aquinoxaline derivative of the invention measured by CV measurement.

FIG. 14 is a graph showing a reduction reaction characteristic of2,3-bis{4-[N-(4-bipheniryl)-N-phenylamino]phenyl}quinoxaline, which is aquinoxaline derivative of the invention measured by CV measurement.

FIG. 15 shows a DSC chart of2,3-bis{4-[N-(4-bipheniryl)-N-phenylamino]phenyl}quinoxaline, which is aquinoxaline derivative of the invention.

FIGS. 16A and 16B show ¹H NMR charts of2,3-bis{4-[N,N-di(4-bipheniryl)amino]phenyl}quinoxaline, which is aquinoxaline derivative of the invention.

FIG. 17 is a graph showing an absorption spectrum of2,3-bis{4-[N-di(4-bipheniryl)amino]phenyl}quinoxaline in a toluenesolution, which is a quinoxaline derivative of the invention.

FIG. 18 is a graph showing current density-luminance characteristics ofa light emitting element in Embodiment 3.

FIG. 19 is a graph showing voltage-luminance characteristics of thelight emitting element in Embodiment 3.

FIG. 20 is a graph showing luminance-current efficiency characteristicsof the light emitting element in Embodiment 3.

FIG. 21 is a graph showing an oxidation reaction characteristic of2,3-bis{4-[N,N-di(4-bipheniryl)amino]phenyl}quinoxaline, which is aquinoxaline derivative of the invention measured by CV measurement.

FIG. 22 is a graph a reduction reaction characteristic of2,3-bis{4-[N,N-di(4-phenylphenyl)]amino}phenyl-1,4-quinoxaline, which isa quinoxaline derivative of the invention measured by CVmeasurement.

FIG. 23 shows a DSC chart of2,3-bis{4-[N,N-di(4-bipheniryl)amino]phenyl}quinoxaline, which is aquinoxaline derivative of the invention.

FIG. 24 is a graph showing current density-luminance characteristics ofa light emitting element in Embodiment 4.

FIG. 25 is a graph showing voltage-luminance characteristics of thelight emitting element in Embodiment 4.

FIG. 26 is a graph showing luminance-current efficiency characteristicsof the light emitting element in Embodiment 4.

FIG. 27 is a graph showing current density-luminance characteristics ofa light emitting element in Embodiment 5.

FIG. 28 is a graph showing voltage-luminance characteristics of thelight emitting element in Embodiment 5.

FIG. 29 is a graph showing luminance-current efficiency characteristicsof the light emitting element in Embodiment 5.

FIG. 30 is a graph showing current density-luminance characteristics ofa light emitting element in Embodiment 6.

FIG. 31 is a graph showing voltage-luminance characteristics of thelight emitting element in Embodiment 6.

FIG. 32 is a graph showing luminance-current efficiency characteristicsof the light emitting element in Embodiment 6.

FIG. 33 is a graph showing a light emission spectrum of the lightemitting element in Embodiment 3.

FIG. 34 is a graph showing a light emission spectrum of the lightemitting element in Embodiment 4.

FIG. 35 is a graph showing a light emission spectrum of the lightemitting element in Embodiment 5.

FIG. 36 is a graph showing a light emission spectrum of the lightemitting element in Embodiment 6.

FIG. 37 is a view showing a light emitting element of the invention.

FIG. 38 is a graph showing current density-luminance characteristics ofa light emitting element in Embodiment 7.

FIG. 39 is a graph showing voltage-luminance characteristics of thelight emitting element in Embodiment 7.

FIG. 40 is a graph showing luminance-current efficiency characteristicsof the light emitting element in Embodiment 7.

FIG. 41 is a graph showing a light emission spectrum of the lightemitting element in Embodiment 7.

BEST MODE FOR CARRYING OUT THE INVENTION

Although the invention will be fully described by way of embodimentmodes and embodiments with reference to the accompanying drawings, it isto be understood that various changes and modifications will be apparentto those skilled in the art. Therefore, unless such changes andmodifications depart from the scope of the invention, they should beconstrued as being included therein.

Embodiment Mode 1

The quinoxaline derivative of the invention is expressed by thefollowing general formula (1).

(in the formula, R¹ to R¹² may be the same or different and eachrepresent any one of a hydrogen atom, a halogen atom, an alkyl group, analkoxyl group, an acyl group, a dialkyl amino group, a diarylaminogroup, a substituted or unsubstituted vinyl group, a substituted orunsubstituted aryl group, and a substituted or unsubstituted heterocyclegroup. R⁹, R¹⁰, and R¹¹ may be combined with R¹⁰, R¹¹, and R¹²respectively to form a condensed ring. Ar¹ represents a substituted orunsubstituted biphenyl group or a substituted or unsubstituted terphenylgroup. Ar² represents a substituted or unsubstituted phenyl group, asubstituted or unsubstituted biphenyl group, a substituted orunsubstituted terphenyl group, or a substituted or unsubstitutedmonocyclic heterocycle group.)

In the general formula (1), each of the substituted biphenyl group, thesubstituted terphenyl group, and the substituted monocyclic heterocyclegroup preferably has an alkyl group or a phenyl group as thesubstituent. As the alkyl group, a methyl group, an ethyl group, anisopropyl group, a tert-butyl group, and the like are cited.

In particular, the quinoxaline derivative of the invention is preferablythe one expressed by the following general formula (2).

(in the formula, R⁹ to R¹² may be the same or different and eachrepresent any one of a hydrogen atom, a halogen atom, an alkyl group, analkoxyl group, an acyl group, a dialkyl amino group, a diarylaminogroup, a substituted or unsubstituted vinyl group, a substituted orunsubstituted aryl group, and a substituted or unsubstituted heterocyclegroup. R⁹, R¹⁰, and R¹¹ may be combined with R¹⁰, R¹¹, and R¹²respectively to form a condensed ring. Ar¹ represents a substituted orunsubstituted biphenyl group or a substituted or unsubstituted terphenylgroup. Ar² represents a substituted or unsubstituted phenyl group, asubstituted or unsubstituted biphenyl group, a substituted orunsubstituted terphenyl group, or a substituted or unsubstitutedmonocyclic heterocycle group.)

Further, in particular, the quinoxaline derivative of the invention ispreferably the one expressed by the following general formula (3).

(in the formula, R⁹ to R¹² may be the same or different and eachrepresent any one of a hydrogen atom, a halogen atom, an alkyl group, analkoxyl group, an acyl group, a dialkyl amino group, a diarylaminogroup, a substituted or unsubstituted vinyl group, a substituted orunsubstituted aryl group, and a substituted or unsubstituted heterocyclegroup. R⁹, R¹⁰, and R¹¹ may be combined with R¹⁰, R¹¹, and R¹²respectively to form a condensed ring. A represents a substituentexpressed by the structure formula (4) or the structure formula (5). Ar²represents a substituted or unsubstituted phenyl group, a substituted orunsubstituted biphenyl group, a substituted or unsubstituted terphenylgroup, or a substituted or unsubstituted monocyclic heterocycle group.)

Further, in particular, the quinoxaline derivative of the invention ispreferably the one expressed by the following general formula (6).

(in the formula, R⁹ to R¹² may be the same or different and eachrepresent any one of a hydrogen atom, a halogen atom, an alkyl group, analkoxyl group, an acyl group, a dialkyl amino group, a diarylaminogroup, a substituted or unsubstituted vinyl group, a substituted ofunsubstituted aryl group, and a substituted or unsubstituted heterocyclegroup. R⁹, R¹⁰, and R¹¹ may be combined with R¹⁰, R¹¹, and R¹²respectively to form a condensed ring. A represents a substituentexpressed by the structure formula (7) or the structure formula (8). Brepresents a hydrogen atom or a substituent expressed by the structureformula (7) or the structure formula (8).)

Further, in particular, the quinoxaline derivative of the invention ispreferably the one expressed by the following general formula (9).

(in the formula, A represents a substituent expressed by the structureformula (10) or the structure formula (11), and B represents a hydrogenatom or a substituent expressed by the structure formula (10) or thestructure formula (11).)

Further, as a specific example of the quinoxaline derivative of theinvention, quinoxaline derivatives expressed by structure formulas (14)to (65) are cited; however, the invention is not limited to them.

Various reactions can be applied to a synthesizing method of thequinoxaline derivative of the invention. For example, a quinoxalinederivative can be made by a synthetic reaction shown in the followingreaction schemes (A-1) and (A-2).

First, a quinoxaline skeleton is formed by a condensation reactionbetween dibenzil substituted by a halogen atom X and 1,2-diaminobenzene. As a halogen atom, bromine, iodine, and chlorine are cited.Considering easiness of handling and appropriate reactivity, bromine ispreferable.

A desired quinoxaline derivative of the invention can be synthesized bycoupling 2 equivalent diarylamine (Ar¹—NH—Ar²) with the obtainedhalogen-substituted quinoxaline by using a palladium catalyst ormonovalent copper in the presence of a base. As the base, an inorganicbase such as potassium carbonate or sodium carbonate, an organic basesuch as a metal alkoxide, or the like can be used. As the palladiumcatalyst, palladium acetate, palladium chloride,bis(dibenzylidineacetone)palladium, or the hie can be used.

It is to be noted that diarylamine (Ar¹—NH—Ar²) in the aforementionedscheme can be synthesized by the following scheme, for example.

First, in the case where Ar¹ is a biphenyl group, desired aryl amine(Ar¹—NH—Ar²; Ar¹ is a biphenyl group) can be obtained by coupling 1equivalent aryl amine (Ar²—NH₂) with halogen-substituted biphenyl ofwhich the second position, the third position, or the fourth position issubstituted by halogen by using a palladium catalyst or monovalentcopper in the presence of a base. As the base, an inorganic base such aspotassium carbonate or sodium carbonate, an organic base such as a metalalkoxide, or the like can be used. As the palladium catalyst, palladiumacetate, palladium chloride, bis(dibenzylidineacetone)palladium, or thelike can be used.

Further, in the case where both Ar¹ and Ar² are biphenyl groups, desiredaryl amine (Ar¹—NH—Ar²; both Ar¹ and Ar² are biphenyl groups) can beobtained by coupling 2 equivalent phenyl boron acid with diphenylaminein which two phenyl groups are halogen-substituted by using a palladiumcatalyst or a nickel catalyst in the presence of a base, as shown in thefollowing synthetic scheme (A-4). As the base, an inorganic base such aspotassium carbonate or sodium carbonate, an organic base such as a metalalkoxide, or the like can be used. As the palladium catalyst, palladiumacetate, palladium chloride, bis(dibenzylidineacetone)palladium, or thelike can be used. This method has an advantage thatN,N-di(4-biphenyl)amine can be synthesized without using 4-aminobiphenylwhich is a harmful substance to human body.

On the other hand, in the case where aryl amine (Ar¹—NH—Ar²) in whichAr¹ is a terphenyl group is synthesized, various terphenyl amines ofwhich substituted positions are different can be synthesized by coupling1 equivalent biphenyl boron acid of which the second position, the thirdposition, or the fourth position is substituted by a boronic acid groupwith aniline of which the second position, the third position, or thefourth position is halogen-substituted by using a palladium catalyst ora nickel catalyst in the presence of a base, as shown in the followingsynthetic scheme (A-5). Then, desired aryl amine (Ar¹—NH—Ar²; Ar¹ is aterphenyl group) can be obtained by coupling the obtained 1 equivalentterphenyl amine with halogen-substituted arene (Ar²—X) by using apalladium catalyst or monovalent copper in the presence of a base, asshown in the following synthetic scheme (A-6). As the base, an inorganicbase such as potassium carbonate or sodium carbonate, an organic basesuch as a metal alkoxide, or the like can be used. As the palladiumcatalyst, palladium acetate, palladium chloride,bis(dibenzylidineacetone)palladium, or the like can be used.

Further, in the case where Ar¹ is a terphenyl group and a center benzenering of the terphenyl group is substituted by an amino group, anilinewhich is substituted by two halogen atoms is coupled with 2 equivalentphenyl boron acid by using a palladium catalyst or nickel catalyst inthe presence of a base as shown in the following synthetic scheme (A-7),then, a terphenyl amine which is a terphenyl group substituted by anamino group in a center benzene ring of the terphenyl group. Then,desired aryl amine (Ar¹—NH—Ar²; Ar¹ is a terphenyl group) can beobtained by coupling the obtained 1 equivalent terphenyl amine withhalogen-substituted arene (Ar²—X) by using a palladium catalyst ormonovalent copper in the presence of a base, as shown in the followingsynthetic scheme (A-8). As the base, an inorganic base such as potassiumcarbonate or sodium carbonate, an organic base such as a metal alkoxide,or the like can be used. As the palladium catalyst, palladium acetate,palladium chloride, bis(dibenzylidineacetone)palladium, or the like canbe used.

It is to be noted that the quinoxaline derivative of the invention canbe purified by recrystallization since the quinoxaline derivative can beobtained as precipitation by a synthetic reaction shown in the syntheticscheme (A-2). That is, since impurities can be prevented from beingmixed due to extraction or the like, a complicated or troublesomepurification process is unnecessary. Therefore, the quinoxalinederivative of the invention can be obtained with high purity.

The quinoxaline derivative of the invention is bipolar and excellent inboth an electron transporting property and a hole transporting property.Therefore, by using the quinoxaline derivative of the invention for anelectronics device, a good electric characteristic can be obtained.Further, the quinoxaline derivative of the invention has a high glasstransition point and excellent heat resistance; therefore, by using thequinoxaline derivative of the invention for an electronics device, anelectronics device which has excellent heat resistance can be obtained.Furthermore, the quinoxaline derivative of the invention is stabilizedwith respect to electrochemical oxidation or reduction; therefore, byusing the quinoxaline derivative of the invention for an electronicsdevice, a long-life electronics device can be obtained.

Embodiment Mode 2

One mode of a light emitting element using the quinoxaline derivative ofthe invention is described below with reference to FIG. 1A.

A light emitting element of the invention has a plurality of layersbetween a pair of electrodes. The plurality of layers are stacked bycombining layers which contain a substance having a high carrierinjecting property and a substance having a high carrier transportingproperty so that a light emitting region is formed apart from theelectrodes, that is, so that carries are recombined at a portion awayfrom the electrodes.

In this embodiment mode, the light emitting element includes a firstelectrode 102; a first layer 103, a second layer 104, a third layer 105,and a fourth layer 106 which are stacked in this order over the firstelectrode 102; and a second electrode 107 provided over the fourth layer106. In this embodiment mode, the first electrode 102 functions as ananode and the second electrode 107 functions as a cathode.

A substrate 101 is used to support the light emitting element. As thesubstrate 101, for example, glass, plastic, or the like can be used.Other materials than those may also be used as long as the lightemitting element can be supported in a manufacturing process.

As the first electrode 102, a metal, an alloy, a conductive compound, ora mixture thereof, each of which has a high work function (specifically,4.0 eV or higher) is preferably used. Specifically, for example, indiumtin oxide (ITO), indium tin oxide containing silicon; indium zinc oxide(IZO) in which zinc oxide (ZnO) is mixed by 2 to 20 wt % into indiumoxide; indium oxide containing 0.5 to 5 wt % of tungsten oxide and 0.1to 1 wt % of zinc oxide (IWZO); or the like can be used. Although theseconductive metal oxide films are generally formed by sputtering, it maybe formed by applying a sol-gel method or the like. Alternatively, gold(Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr),molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), anitride of a metal material (such as TiN), or the like can be used.

The first layer 103 contains a substance having a high hole injectingproperty. Molybdenum oxide (MoO_(x)), vanadium oxide (VO_(x)), rutheniumoxide (RuO_(x)), tungsten oxide (WO_(x)), manganese oxide (MnO_(x)), orthe like can be used. Alternatively, the first layer 103 can be formedof a phthalocyanine-based compound such as phthalocyanine (H₂Pc) orcopper phthalocyanine (CuPc); a high molecule such as poly(ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS); or the like.

Alternatively, a composite material including an organic compound and aninorganic compound may be used for the first layer 103. In particular, acomposite material including an organic compound and an inorganiccompound showing an electron-accepting property with respect to theorganic compound is excellent in a hole injecting property and a holetransporting property since an electron is transferred between theorganic compound and the inorganic compound and carrier density isincreased. In that case, a material having an excellent holetransporting property is preferably used as the organic compound.Specifically, an aromatic amine-based organic compound or acarbazole-based organic compound is preferable. Alternatively, aromatichydrocarbon may be used as the organic compound. As the inorganiccompound, a substance showing an electron accepting property withrespect to an organic compound may be used. Specifically, an oxide of atransition metal is preferable. For example, a metal oxide such astitanium oxide (TiO_(x)), vanadium oxide (VO_(x)), molybdenum oxide(MoO_(x)), tungsten oxide (WO_(x)), rhenium oxide (ReO_(x)), rutheniumoxide (RuO_(x)), chromium oxide (CrO_(x)), zirconium oxide (ZrO_(x)),hafnium oxide (HfO_(x)), tantalum oxide (TaO_(x)), silver oxide(AgO_(x)), or manganese oxide (MnO_(x)) can be used. In the case ofusing a composite material including an organic compound and aninorganic compound for the first layer 103, the first layer 103 can havean ohmic contact with the first electrode 102; therefore, a material ofthe first electrode can be selected regardless of work function.

As a substance for forming the second layer 104, a substance having ahigh hole transporting property, specifically, an aromatic amine-based(that is, one having a bond of benzene ring-nitrogen) compound ispreferable. A material that is widely used includes4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl, derivatives thereofsuch as 4,4′-bis[N-(1-napthyl)-N-phenylamino]biphenyl (hereinafterreferred to as NPB), and star burst aromatic amine compounds such as4,4′,4″-tris(N,N-diphenyl-amino)triphenylamine, and4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine. Thesubstance described here are mainly a substance having a hole mobilityof 10⁻⁶ cm²/Vs or higher. However, other materials than those may alsobe used as long as a substance has a higher hole transporting propertythan an electron transporting property. Note that the second layer 104may be a single layer or a mixed-layer of the above substances, or maybe formed by stacking two or more layers.

The third layer 105 is a layer including a light emitting substance. Inthis embodiment mode, the third layer 105 includes the quinoxalinederivative of the invention described in Embodiment Mode 1. Thequinoxaline derivative of the invention can preferably be applied to alight emitting element as a light emitting substance since thequinoxaline derivative exhibits light emission of blue to blue green.

The fourth layer 106 is formed of a substance having a high electrontransporting property, for example, a metal complex having a quinolineskeleton or a benzoquinoline skeleton and the like, such astris(8-quinolinolato)aluminum (abbreviated to Alq),tris(5-methyl-8-quinolinolato)aluminum (abbreviated to Almq₃),bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbreviated to BeBq₂), orbis(2-methyl-8-quinolinolato)-4-phenylphenolato-aluminum (abbreviated toBAlq). Alternatively, a metal complex having an oxazole-based or athiazole-based ligand, such asbis[2-(2-hydroxyphenyl)-benzoxazolato]zinc (abbreviated to Zn(BOX)₂) orbis[2-(2-hydroxyphenyl)-benzothiazolato]zinc (abbreviated to Zn(BTZ)₂)can be used. Alternatively, other than the metal complexes,2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviated toPBD), 1,3-bis[5-(p-tert-buthylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviated to OXD-7),3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(abbreviated to TAZ),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviated to p-EtTAZ), bathophenanthroline (abbreviated to BPhen),bathocuproin (abbreviated to BCP), or the like can be used. Thesubstances described here are mainly a substance having an electronmobility of 10⁻⁶ cm²/Vs or higher. However, other materials than thosemay also be used as long as a substance has a higher electrontransporting property than a hole transporting property. Note that thefourth layer 106 may be a single layer or may be formed by stacking twoor more layers including the above substances.

The second electrode 107 can be formed of a metal, an alloy, aconductive compound, mixture of these, or the like which has a low workfunction (work function of 3.8 eV or lower). As a specific example ofsuch a cathode material, an element belonging to Group 1 or Group 2 inthe periodic table, that is, an alkali metal such as lithium (Li) orcesium (Cs), an alkaline earth metal such as magnesium (Mg), calcium(Ca), or strontium (Sr), an alloy containing any of these (such as MgAgor AlLi), a rare earth metal such as europium (Eu) or ytterbium (Yb), analloy containing any of these, or the like can be cited. However, when alayer having a function of promoting electron injection is providedbetween the second electrode 107 and a light emitting layer and incontact with the second electrode 107, various conductive materials suchas Al, Ag, ITO, or ITO containing silicon can be used for the secondelectrode 107 regardless of the work function.

For the layer having a function of promoting electron injection, acompound of an alkali metal or an alkaline earth metal, such as lithiumfluoride (LiF), cesium fluoride (CsF), or calcium fluoride (CaF₂) can beused. Alternatively, a layer which includes a substance having anelectron transporting property may be mixed with an alkali metal, analkaline earth metal, an alkali metal compound, or an alkaline earthmetal compound, for example, Alq containing lithium oxide (LiO_(x)),magnesium nitride (MgO_(x)), magnesium (Mg), or lithium (Li) can beused.

The first layer 103, the second layer 104, the third layer 105, and thefourth layer 106 may be formed by, for example, various methods such asan ink jet method, a spin coating method, and the like as well as anevaporation method. Moreover, a different film forming method may beused for each electrode or each layer.

In the light emitting element of the invention having the aforementionedstructure, current flows due to a potential difference generated betweenthe first electrode 102 and the second electrode 107 and holes andelectrons are recombined in the third layer 105 which contains thesubstance having a high light emitting property, thereby light isemitted. That is, the structure is such that a light emitting region isformed in the third layer 105.

Light is extracted to the outside through one or both of the firstelectrode 102 and the second electrode 107. Therefore, one or both ofthe first electrode 102 and the second electrode 107 is formed of asubstance having light transmissivity. If only the first electrode 102is formed of a substance having light transmissivity, light is extractedfrom the substrate side through the first electrode 102 as shown in FIG.1A. If only the second electrode 107 is formed of a substance havinglight transmissivity, light is extracted from an opposite side of thesubstrate side through the second electrode 107 as shown in FIG. 1B. Ifboth of the first electrode 102 and the second electrode 107 are formedof a substance having light transmissivity, light is extracted from bothof the substrate side and the opposite side of the substrate sidethrough the first electrode 102 and the second electrode 107 as shown inFIG. 1C.

The structure of the layers provided between the first electrode 102 andthe second electrode 107 is not limited to the aforementioned structure.Other structures than the aforementioned one may be applied as long asthe structures are as follows: a light emitting region where holes andelectrons are recombined is provided apart from the first electrode 102and the second electrode 107 so that quenching due to approximation ofthe light emitting region and the metal is suppressed.

In other words, the stacked structure of the layers is not particularlylimited, and a layer which includes a substance having a high electrontransporting property, a substance having a high hole transportingproperty, a substance having a high electron injecting property, asubstance having a high hole injecting property, a substance having abipolar property (a substance having a high electron transportingproperty and a high hole transporting property), a hole blockingmaterial, or the like may be freely combined with the quinoxalinederivative of the invention.

A light emitting element shown in FIG. 2 has a structure in which afirst layer 303 which includes a substance having a high electrontransporting property, a second layer 304 which includes a lightemitting substance, a third layer 305 which includes a substance havinga high hole transporting property, a fourth layer 306 which includes asubstance having a high hole injecting property, and a second electrode307 functioning as an anode are stacked in this order over a firstelectrode 302 functioning as a cathode. A reference numeral 301 denotesa substrate.

In this embodiment mode, the light emitting element is manufactured overthe substrate made of glass, plastic, or the like. By manufacturing aplurality of such light emitting elements over one substrate, a passivelight emitting device can be manufactured. Alternatively, for example, athin film transistor (TFT) may be formed over a substrate made of glass,plastic, or the like, and the light emitting elements may bemanufactured over an electrode electrically connected to the TFT. Thus,an active matrix light emitting device in which the driving of the lightemitting element is controlled by the TFT can be manufactured. Thestructure of the TFT is not particularly limited. Either a staggered TFTor an inverted staggered TFT is applicable. Further, the crystallinityof a semiconductor used for the TFT is not particularly limited. Eitheran amorphous semiconductor or a crystalline semiconductor may be used. Adriver circuit formed over a TFT array substrate may be formed by usingone or both of an N-type TFT and a P-type TFT.

The quinoxaline derivative of the invention can be used as a lightemitting layer without including another light emitting substance asdescribed in this embodiment mode since the quinoxaline derivative isbipolar and a light emitting material.

Further, since the quinoxaline derivative of the invention is bipolar, alight emitting element in which a light emitting region is rarelylocated at an interface of stacked films, and which shows favorablecharacteristics with few changes in light emission spectrum and littledecrease in light emission efficiency due to an interaction such asexciplex can be manufactured.

Further, an amorphous film which includes few microcrystallinecomponents can be obtained since microcrystalline components are hardlyincluded during a film formation. That is, the film has a favorablequality; therefore, a light emitting element with few element defectssuch as a dielectric breakdown due to electric field concentration canbe manufactured.

Further, the quinoxaline derivative of the invention is a material whichis bipolar and excellent in a carrier transporting property (an electrontransporting property and a hole transporting property); therefore, whenthe quinoxaline derivative is used for a light emitting element, adriving voltage of the light emitting element can be reduced and thusthe power consumption can be lowered.

Further, by using the quinoxaline derivative of the invention, which hasa high glass transition point, a light emitting element having high heatresistance can be obtained.

Further, the quinoxaline derivative of the invention is stabilized withrespect to oxidizing reactions and reductive reactions occurringalternately. That is, the quinoxaline derivative is electrochemicallystabilized. Therefore, by using the quinoxaline derivative of theinvention for a light emitting element, a long-life light emittingelement can be obtained.

It is to be noted that the quinoxaline derivative of the invention in asolution state exhibits light emission of blue to blue green in a shortwavelength region, and the quinoxaline derivative in a solid state alsoexhibits light emission in a short wavelength region. This is explainedas follows. In the quinoxaline derivative of the invention, not a planarcondensed aromatic ring such as a naphthyl group or a fluorenyl groupbut a twisted biphenyl group is connected to an amino group. It isconsidered that the quinoxaline derivative hardly assembles due to thetwist form of the biphenyl group in a solid state and light emissioncolors almost corresponds to each other between in a solid state and ina solution state. That is, the quinoxaline derivative of the inventionhas such a characteristic that a peak of light emission spectrum isalmost the same between in a solution state and in a solid state;therefore, by using the quinoxaline derivative in a thin film state(solid state) for a light emitting element, light emission with a shortwavelength can be obtained.

Embodiment Mode 3

In this embodiment mode, description is made of a light emitting elementhaving a different structure from that described in Embodiment Mode 2.

The third layer 105 described in Embodiment Mode 2 is formed bydispersing the quinoxaline derivative of the invention on anothersubstance, thereby light emission can be obtained from the quinoxalinederivative of the invention. A light emitting element exhibiting lightemission of blue to blue green can be obtained since the quinoxalinederivative of the invention exhibits light emission of blue to bluegreen.

Here, various materials can be used as a substance on which thequinoxaline derivative of the invention is dispersed. In addition to thesubstance having a high hole transporting property and the substancehaving a high electron transporting property, which are described inEmbodiment Mode 2, 4,4′-di(N-carbazolyl)-biphenyl (abbreviated to CBP),2,2′,2″-(1,3,5-benzenetri-yl)-tris[1-phenyl-1H-benzimidazole](abbreviated to TPBI), 9,10-di(2-naphthyl)anthracene (abbreviated toDNA), 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviated tot-BuDNA), and the like are cited.

The quinoxaline derivative of the invention is a material which isbipolar and excellent in a carrier transporting property (an electrontransporting property and a hole transporting property); therefore, whenthe quinoxaline derivative is used for a light emitting element, adriving voltage of the light emitting element can be reduced and thepower consumption can be lowered.

Further, using the quinoxaline derivative of the invention allows toobtain a light emitting element having high heat resistance since thequinoxaline derivative of the invention has a high glass transitionpoint.

Further, the quinoxaline derivative of the invention is stabilized withrespect to oxidizing reactions and reductive reactions occurringalternately. That is, the quinoxaline derivative is electrochemicallystabilized. Therefore, using the quinoxaline derivative of the inventionallows to obtain a long-life light emitting element.

It is to be noted that the structure described in Embodiment Mode 2 canbe appropriately used for layers other than the third layer 105.

Embodiment Mode 4

In this embodiment mode, description is made of a light emitting elementhaving a different structure from those described in Embodiment Modes 2and 3.

The third layer 105 described in Embodiment Mode 2 is formed bydispersing a light emitting substance on the quinoxaline derivative ofthe invention, thereby, light emission can be obtained from the lightemitting substance.

The quinoxaline derivative of the invention is bipolar, and has afavorable film quality since microcrystalline components are hardlyincluded during a film formation; therefore, the quinoxaline derivativecan be preferably used as a material on which another light emittingsubstance is dispersed.

In the case where the quinoxaline derivative of the invention is used asa material on which another light emitting substance is dispersed, alight emission color due to the light emitting substance can beobtained. Further, a mixed color of a light emission color due to thequinoxaline derivative of the invention and a light emission color dueto the light emitting substance dispersed in the quinoxaline derivativecan also be obtained.

Here, various materials can be used as a light emitting substancedispersed on the quinoxaline derivative of the invention. Specifically,a fluorescent substance such as4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran(abbreviated to DCM1),4-(dicyanomethylene)-2-methyl-6-(julolidine-4-yl-vinyl)-4H-pyran(abbreviated to DCM2), N,N′-dimethylquinacridone (abbreviated to DMQd),9,10-diphenylanthracene (abbreviated to DPA); 5,12-diphenyltetracene(abbreviated to DPT), coumarin 6, perylene, or rubrene, or aphosphorescent substance such asbis[2-(2′-benzothienyl)pyridinato-N,C^(3′)](acetylacetonato)iridium(abbreviated to Ir(btp)₂(acac)) can be used.

Further, as a light emitting substance dispersed on the quinoxalinederivative of the invention, an organometallic complex having astructure expressed by the following general formula (101) can be used.

(in the formula, R¹ to R⁵ each represent any one of hydrogen, a halogenelement, an acyl group, an alkyl group, an alkoxyl group, an aryl group,a cyano group, and a heterocycle group. Ar represents an aryl group or aheterocycle group. M represents an element which belongs to Group 9 orGroup 10.)

In the general formula (101), Ar is preferably an aryl group or aheterocycle group having an electron-withdrawing substituent. Since Aris a group having an electron-withdrawing substituent, a phosphorescentorganometallic complex having higher light emission intensity can beobtained.

In particular, an organometallic complex having a structure expressed bythe following general formula (102) is preferable.

(in the formula, R¹¹ represents any one of alkyl groups having 1 to 4carbon atoms. R¹² to R¹⁵ each represent any one of hydrogen, a halogenelement, an acyl group, an alkyl group, an alkoxyl group, an aryl group,a cyano group, and a heterocycle group. Further, R¹⁶ to R¹⁹ eachrepresent any one of hydrogen, an acyl group, an alkyl group, an alkoxylgroup, an aryl group, a heterocycle group, and an electron-withdrawingsubstituent. M represents an element which belongs to Group 9 or Group10.)

In the general formula (102), at least one of R¹⁶ to R¹⁹ is preferablyan electron-withdrawing substituent. Accordingly, a phosphorescentorganometallic complex having higher light emission intensity can beobtained.

Further, in particular, an organometallic complex is preferably the onehaving a structure expressed by the following general formula (103).

(in the formula, R²² to R³⁴ each represent any one of hydrogen, ahalogen element, an acyl group, an alkyl group, an alkoxyl group, anaryl group, a cyano group, a heterocycle group, and anelectron-withdrawing substituent. M represents an element which belongsto Group 9 or Group 10.)

In the general formula (103), at least one of R²⁶ to R²⁹ is preferablyan electron-withdrawing substituent. Accordingly, a phosphorescentorganometallic complex having higher light emission intensity can beobtained.

An organometallic complex expressed by the general formula (104) iscited as an organometallic complex having a structure expressed by theaforementioned general formula (101).

(in the formula, R¹ to R⁵ each represent any one of hydrogen, a halogenelement, an acyl group, an alkyl group, an alkoxyl group, an aryl group,a cyano group, and a heterocycle group. Ar represents an aryl group or aheterocycle group. M represents an element which belongs to Group 9 orGroup 10. When M is a Group 9 element, n=2 is satisfied, whereas when Mis a Group 10 element, n=1 is satisfied. L represents any one of amonoanionic ligand having a beta-diketone structure, a monoanionicbidentate chelate ligand having a carboxyl group, and a monoanionicbidentate chelate ligand having a phenol hydroxyl group.)

In the general formula (104), Ar is preferably an aryl group or aheterocycle group having an electron-withdrawing substituent. Since Aris a group having an electron-withdrawing substituent, a phosphorescentorganometallic complex having higher light emission intensity can beobtained.

In particular, an organometallic complex expressed by the followinggeneral formula (105) is preferable.

(in the formula, R¹¹ represents any one of alkyl groups having 1 to 4carbon atoms. R¹² to R¹⁵ each represent any one of hydrogen, a halogenelement, an acyl group, an alkyl group, an alkoxyl group, an aryl group,a cyano group, and a heterocycle group. Further, R¹⁶ to R¹⁹ eachrepresent any one of hydrogen, an acyl group, an alkyl group, an alkoxylgroup, an aryl group, a heterocycle group, and an electron-withdrawingsubstituent. M represents an element which belongs to Group 9 or Group10. When M is a Group 9 element, n=2 is satisfied, whereas when M is aGroup 10 element, n=1 is satisfied. L represents any one of amonoanionic ligand having a beta-diketone structure, a monoanionicbidentate chelate ligand having a carboxyl group, and a monoanionicbidentate chelate ligand having a phenol hydroxyl group.)

In the general formula (105), at least one of R¹⁶ to R¹⁹ is preferablyan electron-withdrawing substituent. Accordingly, a phosphorescentorganometallic complex having higher light emission intensity can beobtained.

Further, in particular, an organometallic complex expressed by thefollowing general formula (106) is preferable.

(in the formula, R²² to R³⁴ each represent any one of hydrogen, ahalogen element, an acyl group, an alkyl group, an alkoxyl group, anaryl group, a cyano group, a heterocycle group, and anelectron-withdrawing substituent. M represents an element which belongsto Group 9 or Group 10. When M is a Group 9 element, n=2 is satisfied,whereas when M is a Group 10 element, n=1 is satisfied. L represents anyone of a monoanionic ligand having a beta-diketone structure, amonoanionic bidentate chelate ligand having a carboxyl group, and amonoanionic bidentate chelate ligand having a phenol hydroxyl group.)

In the general formula (106), at least one of R²⁶ to R²⁹ is preferablyan electron-withdrawing substituent. Accordingly, a phosphorescentorganometallic complex having higher light emission intensity can beobtained.

In the organometallic complexes having the structures expressed by thegeneral formulas (101) to (103), and the organometallic complexexpressed by the general formulas (104) to (106), theelectron-withdrawing substituent is preferably a halogen group, ahaloalkyl group, or a cyano group. Accordingly, chromaticity and quantumefficiency of the organometallic complex are improved. Further, a fluorogroup is particularly preferable among halogen groups and atrifluoromethyl group is particularly preferable among halo alkylgroups. Accordingly, electrons can be trapped efficiently.

In the organometallic complexes having the structures expressed by thegeneral formulas (101) to (103), and the organometallic complexesexpressed by the general formulas (104) to (106), a central metal M ispreferably a heavy metal, and more preferably, iridium or platinum.Accordingly, a heavy atom effect can be obtained.

In the general formulas (104) to (106), a ligand L may be any of amonoanionic ligand having a beta-diketone structure, a monoanionicbidentate chelate ligand having a carboxyl group, and a monoanionicbidentate chelate ligand having a phenol hydroxyl group. However, anyone of monoanionic ligands expressed by the following structure formulas(107) to (113) is preferable. These monoanionic chelate ligands areuseful since they have high coordinative ability and are inexpensive.

Organometallic complexes expressed by the structure formulas (114) to(126) are cited as specific examples of the organometallic complexesexpressed by the aforementioned general formulas (101) to (106)

It is to be noted that a light emitting element in which light emissionis obtained from a triplet excitation state by adding the aforementionedorganometallic complex, which is a phosphorescent substance, to thequinoxaline derivative of the invention has a low driving voltage andhigh current efficiency. Therefore, a light emitting element consuminglow power can be obtained.

The quinoxaline derivative of the invention is a material which isbipolar and excellent in a carrier transporting property (an electrontransporting property and a hole transporting property); therefore, whenthe quinoxaline derivative of the invention is used for a light emittingelement, a driving voltage of the light emitting element can be lowered.

Further, by using the quinoxaline derivative of the invention, which hasa high glass transition point, a light emitting element having high heatresistance can be obtained.

Further, the quinoxaline derivative of the invention is stabilized withrespect to oxidizing reactions and reductive reactions occurringalternately. That is, the quinoxaline derivative of the invention iselectrochemically stabilized. Therefore, by using the quinoxalinederivative of the invention for a light emitting element, a long-lifelight emitting element can be obtained.

Further, in particular, by applying a light emitting layer in which aspecific organometallic complex expressed by the aforementioned generalformula (101) is dispersed on the quinoxaline derivative of theinvention, a long-life light emitting element consuming significantlylow power can be obtained.

It is to be noted that the quinoxaline derivative of the invention in asolution state exhibits light emission of blue to blue green in a shortwavelength region, and the quinoxaline derivative in a solid state alsoexhibits light emission in a short wave length region. This is explainedas follows. In the quinoxaline derivative of the invention, not a planarcondensed aromatic ring such as a naphthyl group or a fluorenyl groupbut a twisted biphenyl group is connected to an amino group. It isconsidered that the quinoxaline derivative hardly assembles due to thetwist form of the biphenyl skeleton in a solid state and light emissioncolors almost corresponds to each other between in a solid state and ina solution state. That is, the quinoxaline derivative of the inventionhas such a characteristic that a peak of light emission spectrum isalmost the same between in a solution state and in a solid state;therefore, by using the quinoxaline derivative in a thin film state(solid state) for a light emitting element, alternatives of a lightemitting substance which is dispersed on the quinoxaline derivative areincreased. Specifically, in the case of using a phosphorescent substanceas a light emitting substance which is dispersed, a light emissionspectrum of the phosphorescent substance preferably has a peak at 560 nmto 700 nm. Meanwhile, in the case of using a fluorescent substance, alight emission spectrum of the phosphorescent substance preferably has apeak at 500 nm to 700 nm, and more preferably, 500 nm to 600 nm.

It is to be noted that the structure described in Embodiment Mode 2 canbe used for layers other than the third layer 105.

Embodiment Mode 5

In this embodiment mode, a mode in which the quinoxaline derivative ofthe invention is used for an active layer of a vertical transistor (SIT)which is a kind of an organic semiconductor element, is described as anexample.

The element has a structure in which a thin active layer 1202 includingthe quinoxaline derivative of the invention is sandwiched between asource electrode 1201 and a drain electrode 1203, and a gate electrode1204 is embedded in the active layer 1202, as shown in FIG. 7. The gateelectrode 1204 is electrically connected to a unit for applying a gatevoltage, and the source electrode 1201 and the drain electrode 1203 areelectrically connected to a unit for controlling a source-drain voltage.

In such an element structure, when a voltage is applied between thesource and the drain under the condition where a gate voltage is notapplied, a current flows (be in an ON state). When a gate voltage isapplied in this state, a depletion layer is generated on the peripheryof the gate electrode 1204, thereby a current does not flow (be in anOFF state). With the aforementioned mechanism, the element operates as atransistor.

In a vertical transistor, a material which has both a carriertransporting property and an excellent film quality is required for anactive layer similarly to a light emitting element. The quinoxalinederivative of the invention is useful since it sufficiently meets therequirement.

Embodiment Mode 6

In this embodiment mode, a light emitting device manufactured using thequinoxaline derivative of the invention is described with reference toFIGS. 3A and 3B.

It is to be noted that FIG. 3A is a top plan view showing a lightemitting device and FIG. 3B is a cross-sectional view of FIG. 3A takenalong lines A-A′ and B-B′. Reference numeral 601 denotes a drivercircuit portion (source side driver circuit); 602 denotes a pixelportion; and 603 denotes a driver circuit portion (gate side drivercircuit), which are indicated by dotted lines. Reference numeral 604denotes a sealing substrate; 605 denotes a sealing material; and aportion surrounded by the sealing material 605 corresponds to a space607.

It is to be noted that a lead wiring 608 is a wiring for transmitting asignal to be inputted to the source side driver circuit 601 and the gateside driver circuit 603 and receives a video signal, a clock signal, astart signal, a reset signal, and the like from an FPC (flexible printedcircuit) 609 that is an external input terminal. It is to be noted thatonly the FPC is shown here; however, the FPC may be provided with aprinted wiring board (PWB). The light emitting device in thisspecification includes not only a light emitting device itself but alsoa light emitting device attached with an FPC or a PWB.

Subsequently, a cross-sectional structure is described with reference toFIG. 3B. The driver circuit portion and the pixel portion are formedover an element substrate 610. Here, the source side driver circuit 601which is the driver circuit portion and one pixel in the pixel portion602 are shown.

It is to be noted that a CMOS circuit, which is a combination of ann-channel TFT 623 and a p-channel TFT 624, is formed as the source sidedriver circuit 601. A TFT for forming the driver circuit may be formedusing various circuits such as a PMOS circuit or an NMOS circuit.Although a driver integration type in which a driver circuit is formedover a substrate is described in this embodiment mode, a driver circuitis not necessarily formed over a substrate and can be formed outside asubstrate. Further, crystallinity of a semiconductor used for a TFT isnot particularly limited. Either an amorphous semiconductor or acrystalline semiconductor may be used.

The pixel portion 602 has a plurality of pixels, each of which includesa switching TFT 611, a current control TFT 612, and a first electrode613 which is electrically connected to a drain of the current controlTFT 612. It is to be noted that an insulator 614 is formed so as tocover an end portion of the first electrode 613. Here, a positivephotosensitive acrylic resin film is used for the insulator 614.

The insulator 614 is formed so as to have a curved surface havingcurvature at an upper end portion or a lower end portion thereof inorder to make the coverage favorable. For example, in the case of usingpositive photosensitive acrylic as a material for the insulator 614, theinsulator 614 is preferably formed so as to have a curved surface with acurvature radius (0.2 μm to 3 μm) only at the upper end portion thereof.Either a negative type which becomes insoluble in an etchant by lightirradiation or a positive type which becomes soluble in an etchant bylight irradiation can be used as the insulator 614.

A layer 616 including a light emitting substance and a second electrode617 are formed over the first electrode 613. Here, a material having ahigh work function is preferably used as a material for the firstelectrode 613 which serves as an anode. For example, the first electrode613 can be formed by using stacked layers of a titanium nitride film anda film containing aluminum as its main component; a three-layerstructure of a titanium nitride film, a film including aluminum as itsmain component, and another titanium nitride film; or the like as wellas a single-layer film such as an ITO film, an indium tin oxide filmcontaining silicon, an indium oxide film containing zinc oxide of 2 to20 wt %, a titanium nitride film, a chromium film, a tungsten film, a Znfilm, or a Pt film. When the first electrode 613 has a stacked layerstructure, it can have low resistance as wiring and form a favorableohmic contact. Further, the first electrode 613 can function as ananode.

In addition, the layer 616 including a light emitting substance isformed by various methods such as an evaporation method using anevaporation mask, an ink-jet method, and a spin coating method. Thelayer 616 including a light emitting substance has the quinoxalinederivative of the invention described in Embodiment Mode 1. Further, thelayer 616 including a light emitting substance may include anothermaterial such as a low molecular-based material, a medium molecularmaterial (including an oligomer and a dendrimer), or a highmolecular-based material. In addition, as a material used for the layerincluding a light emitting substance, a single layer or stacked layersof an organic compound is generally used. However, the invention alsoincludes a structure in which an inorganic compound is used for a partof a film made of the organic compound.

As a material used for the second electrode 617 which is formed over thelayer 616 including a light emitting substance and serves as a cathode,a material having a low work function (Al, Mg, Li, Ca, or an alloy or acompound of these such as MgAg, MgIn, AlLi, LiF, or CaF₂) is preferablyused. In the case where light generated in the layer 616 including alight emitting substance is transmitted through the second electrode617, stacked layers of a metal thin film and a light transmissiveconductive film (of ITO, indium oxide containing zinc oxide of 2 to 20wt %, indium tin oxide containing silicon, zinc oxide (ZnO), or thelike) are preferably used as the second electrode 617.

By attaching the sealing substrate 604 to the element substrate 610 withthe sealing material 605, a light emitting element 618 is provided inthe space 607 surrounded by the element substrate 610, the sealingsubstrate 604, and the sealing material 605. It is to be noted that thespace 607 is filled with a filler. There is also a case where the space607 is filled with the sealing material 605 as well as an inert gas(nitrogen, argon, or the like).

It is to be noted that an epoxy-based resin is preferably used as thesealing material 605. The material desirably allows as little moistureand oxygen as possible to penetrate. As the sealing substrate 604, aplastic substrate made of FRP (Fiberglass-Reinforced Plastics), PVF(polyvinyl fluoride), Myler, polyester, acrylic, or the like can be usedbesides a glass substrate or a quartz substrate.

As described above, a light emitting device manufactured using thequinoxaline derivative of the invention can be obtained.

A light emitting device of the invention can have favorablecharacteristics since the quinoxaline derivative of the inventiondescribed in Embodiment Mode 1 is used for the light emitting device.Specifically, a highly heat resistant light emitting device can beobtained.

Further, a long-life light emitting device can be obtained since thequinoxaline derivative of the invention is electrochemically stable.

Further, the quinoxaline derivative of the invention is a material whichis bipolar and excellent in a carrier transporting property (an electrontransporting property and a hole transporting property); therefore, whenthe quinoxaline derivative of the invention is used for a light emittingelement, a driving voltage of the light emitting element and the powerconsumption of a light emitting device can be lowered. In particular, inthe case of using a phosphorescent substance as a light emittingsubstance, a light emitting device which has high light emissionefficiency and consumes lower power can be obtained.

In this embodiment mode, description is made of an active light emittingdevice for controlling driving of a light emitting element by atransistor. Alternatively, a passive light emitting device which drivesa light emitting element without particularly providing an element fordriving such as a transistor may also be used. FIG. 4 shows aperspective view of a passive light emitting device which ismanufactured by applying the invention. In FIG. 4, a layer 955 includinga light emitting substance is provided between an electrode 952 and anelectrode 956 over a substrate 951. An edge portion of the electrode 952is covered with an insulating layer 953. Then, a partition layer 954 isprovided over the insulating layer 953. A side wall of the partitionlayer 954 slopes so that a distance between one side wall and the otherside wall becomes narrow toward a substrate surface. In other words, across section of the partition layer 954 in the direction of a shortside is trapezoidal, and a base (side facing in the same direction as aplane direction of the insulating layer 953 and in contact with theinsulating layer 953) is shorter than an upper side (side facing in thesame direction as the plane direction of the insulating layer 953 andnot in contact with the insulating layer 953). By providing thepartition layer 954 in this manner, a defect of the light emittingelement due to static electricity or the like can be prevented. Inaddition, the passive light emitting device can also be driven with lowpower consumption when it includes the light emitting element of theinvention which operates at a low driving voltage.

Embodiment Mode 7

In this embodiment mode, description is made of an electronic applianceof the invention including the light emitting device described inEmbodiment Mode 4. The electronic appliance of the invention includingthe quinoxaline derivative described in Embodiment Mode 1 has a displayportion which has high heat resistance and a long life, and consumeslower power.

As an electronic appliance including a light emitting elementmanufactured using the quinoxaline derivative of the invention, a camerasuch as a video camera or a digital camera, a goggle type display, anavigation system, an audio reproducing device (car audio componentstereo, audio component stereo, or the hie), a computer, a game machine,a portable information terminal (mobile computer, mobile phone, portablegame machine, electronic book, or the like), and an image reproducingdevice provided with a recording medium (specifically, a device capableof reproducing a recording medium such as a Digital Versatile Disc (DVD)and provided with a display device that can display the image), and thelike are given. Specific examples of these electronic appliances areshown in FIGS. 5A to 5D.

FIG. 5A shows a television device according to the invention, whichincludes a housing 9101, a supporting base 9102, a display portion 9103,a speaker portion 9104; a video input terminal 9105, and the like. Inthe television device, the display portion 9103 has light emittingelements similar to those described in Embodiment Modes 2 to 4, whichare arranged in matrix. One feature of the light emitting element isthat driving with a low voltage can be performed and the life is long.In addition, the heat resistance is high. The display portion 9103 whichincludes the light emitting elements has a similar feature. Therefore,in the television device, image quality is hardly deteriorated and lowpower consumption is achieved. With such a feature, deteriorationcompensation functions and power source circuits can be significantlyreduced or downsized in the television device; therefore, small size andlightweight housing 9101 and supporting base 9102 can be achieved. Inthe television device according to the invention, low power consumption,high image quality, and small size and lightweight are achieved;therefore, a product which is suitable for living environment can beprovided.

FIG. 5B shows a computer according to the invention, which includes amain body 9201, a housing 9202, a display portion 9203, a keyboard 9204,an external connection port 9205, a pointing mouse 9206, and the like.In the computer, the display portion 9203 has light emitting elementssimilar to those described in Embodiment Modes 2 to 4, which arearranged in matrix. One feature of the light emitting element is thatdriving with a low voltage can be performed and the life is long. Inaddition, the heat resistance is high. The display portion 9203 whichincludes the light emitting elements has a similar feature. Therefore,in the computer, image quality is hardly deteriorated and lower powerconsumption is achieved. With such a feature, a deteriorationcompensation function and the number of power source circuits can besignificantly removed or reduced in the computer; therefore, small sizeand lightweight main body 9201 and housing 9202 can be achieved. In thecomputer according to the invention, low power consumption, high imagequality, and small size and lightweight are achieved; therefore, aproduct which is suitable for living environment can be provided.

FIG. 5C shows a mobile phone according to the invention, which includesa main body 9401, a housing 9402, a display portion 9403, an audio inputportion 9404, an audio output portion 9405, an operation key 9406, anexternal connection port 9407, an antenna 9408, and the like. In themobile phone, a display portion 9403 has light emitting elements similarto those described in Embodiment Modes 2 to 4, which are arranged inmatrix. Another feature of the light emitting element is that drivingwith a low voltage can be performed and the life is long. In addition,the heat resistance is high. The display portion 9403 which includes thelight emitting elements has a similar feature. Therefore, in the mobilephone, image quality is hardly deteriorated and lower power consumptionis achieved. With such a feature, a deterioration compensation functionand the number of power source circuits can be significantly removed orreduced in the mobile phone; therefore, a small size and lightweight ofthe main body 9401 and the housing 9402 can be achieved. In the mobilephone according to the invention, low power consumption, high imagequality, and a small size and lightweight are achieved; therefore, aproduction which is suitable for carrying can be provided.

FIG. 5D shows a camera according to the invention, which includes a mainbody 9501, a display portion 9502, a housing 9503, an externalconnection port 9504, a remote control receiving portion 9505, an imagereceiving portion 9506, a battery 9507, an audio input portion 9508,operation keys 9509, an eye piece portion 9510, and the like. In thecamera, the display portion 9502 has light emitting elements similar tothose described in Embodiment Modes 2 to 4, which are arranged inmatrix. One feature of the light emitting element is that driving with alow voltage can be performed and the life is long. In addition, the heatresistance is high. The display portion 9502 which includes the lightemitting elements has a similar feature. Therefore, in the camera, imagequality is hardly deteriorated and lower power consumption can beachieved. With such a feature, deterioration compensation functions andpower source circuits can be significantly reduced or downsized in thecamera; therefore, small size and lightweight main body 9501 can beachieved. In the camera according to the present invention, low powerconsumption, high image quality, and small size and lightweight areachieved; therefore, a product which is suitable for carrying can beprovided.

As described above, the applicable range of the light emitting device ofthe invention is so wide that the light emitting device can be appliedto electronic appliances in various fields. By using the quinoxalinederivative of the invention, electronic appliances which have displayportions consuming low power and having a long life and high heatresistance can be provided.

The light emitting device of the invention can also be used as alighting installation. One mode using the light emitting element of theinvention as the lighting device is described with reference to FIG. 6.

FIG. 6 shows an example of a liquid crystal display device using thelight emitting device of the invention as a backlight. The liquidcrystal display device shown in FIG. 6 includes a housing 901, a liquidcrystal layer 902, a backlight 903, and a housing 904, and the liquidcrystal layer 902 is connected to a driver IC 905. The light emittingdevice of the invention is used for the backlight 903, and current issupplied through a terminal 906.

By using the light emitting device of the invention as the backlight ofthe liquid crystal display device, a backlight with reduced powerconsumption can be obtained. The light emitting device of the inventionis a lighting device with plane light emission, and can have a largearea. Therefore, the backlight can have a large area, and a liquidcrystal display device having a large area can be obtained. Furthermore,the light emitting device of the invention has a thin shape and consumeslow power; therefore, a thin shape and low power consumption of adisplay device can also be achieved. Since the light emitting device ofthe invention has a long life and an excellent heat resistance, a liquidcrystal display device using the light emitting device also has a longlife and an excellent heat resistance.

Embodiment 1

In this embodiment, a synthesis example of2,3-bis{4-[N-(4-bipheniryl)-N-phenylamino]phenyl}quinoxaline(hereinafter referred to as BPAPQ), which is the quinoxaline derivativeof the invention expressed by the following structure formula (14), isspecifically shown.

[Step 1]

A synthesis method of 2,3-bis(4-bromophenyl)quinoxaline is described. Asynthesis scheme of 2,3-bis(4-bromophenyl)quinoxaline is shown in (B-1).

In a nitrogen atmosphere, a chloroform solution (200 mL) containing 30.0g (81.5 mmol) of 4,4′-dibromobenzyl and 9.00 g (83.2 mmol) ofo-phenylenediamine is refluxed at 80° C. for three hours. The reactionsolution is washed with water after being cooled to a room temperature.The obtained aqueous phase is subjected to extraction with chloroform,and the solution obtained by extraction is washed with saturated salinetogether with the organic phase. After the organic phase is dried withmagnesium sulfate, the mixture is subjected to suction filtration andthe filtrate is condensed. Accordingly, 33 g (yield: 92%) of2,3-bis(4-bromophenyl)quinoxaline which is an object is obtained as awhite solid.

[Step 2]

A synthesis method of N-(4-biphenylyl)-N-phenylamine is described. Asynthesis scheme of N-(4-biphenylyl)-N-phenylamine is shown in (B-2).

In a nitrogen atmosphere, a xylene suspension (150 mL) containing 20.0 g(85.8 mmol) of 4-bromobiphenyl, 16.0 g (172 mmol) of anyline, 0.19 g(0.86 mmol) of palladium acetate, and 23.7 g (172 mmol) of potassiumcarbonate, to which 5.2 g (2.5 mmol) of tri-tert-butylphosphine (10%hexane solution) is added, is refluxed at 120° C. for ten hours. Aftercompletion of reaction, the reaction mixture is washed with water and anaqueous phase is subjected to extraction with toluene. The toluene layeris washed with saturated saline together with an organic phase, and theorganic layer is dried with magnesium sulfate. Then, the mixture issubjected to suction filtration and the filtrate is condensed. Theobtained residue is purified by silica gel column chromatography(developing solution: toluene). The obtained solution is condensed toobtain 13.5 g (yield: 64%) of N-(4-biphenylyl)-N-phenylamine as a whitesolid.

[Step 3]

A synthesis method of2,3-bis{4-[N-(4-biphenylyl)-N-phenylamino]phenyl}quinoxaline(hereinafter referred to as BPAPQ) is described. A synthesis scheme ofBPAPQ is shown in (B-3).

In a nitrogen atmosphere, a toluene suspension (80 mL) containing 5.0 g(11.4 mmol) of 2,3-bis(4-bromophenyl)quinoxaline, 6.1 g (25.0 mmol) ofN-(4-biphenylyl)-N-phenylamine, 0.33 g (0.58 mmol) ofbis(dibenzylidineacetone)palladium(0), and 5.5 g (56.8 mmol) oftert-butoxy sodium, to which 1.2 g (0.58 mmol) oftri-tert-butylphosphine (10% hexane solution) is added, is heated at 80°C. for seven hours. After completion of reaction, the reaction mixtureis cooled to a room temperature and the precipitate is collected bysuction filtration. The obtained filtrate is dissolved in toluene, thesolution is subjected to suction filtration through celite, Florisil,and alumina, and the filtrate is condensed. The obtained residue isrecrystallized with chloroform and hexane to obtain 8.1 g (yield: 78%)of BPAPQ as a yellow powdered solid.

An analysis result of BPAPQ by a proton nuclear magnetic resonancespectroscopy (¹H NMR) is as follows. ¹H NMR (300 MHz, CDCl₃);δ=8.16-8.13 (m, 2H), 7.75-7.72 (m, 2H), and 7.58-7.04 (m, 36H). FIG. 8Ashows an NMR chart of BPAPQ, and FIG. 8B shows an enlarged NMR chart ofa part of 6 to 9 ppm.

Further, a decomposition temperature (Td) of BPAPQ is measured by athermo-gravimetric/differential thermal analyzer (TG/DTA 320,manufactured by Seiko Instruments Inc.). Then, it is found that the Tdis 436° C. and BPAPQ shows preferable heat resistance.

Further, the glass transition point is measured by a differentialscanning calorimeter (DSC, Pyris 1, manufactured by Perkin Elmer Co.,Ltd.). After the sample is heated to 300° C. at 40° C./min to be melted,it is cooled to a room temperature at 40° C./min. After that, thetemperature is risen up to 300° C. at 10° C./min, and thus, a DSC chartshown in FIG. 15 is obtained. According to this chart, it is found thatthe glass transition point (Tg) of BPAPQ is 114° C. and the meltingpoint is 268° C. Therefore, it is found that BPAPQ has a high glasstransition point.

FIG. 9 shows an absorption spectrum of the toluene solution of BPAPQ,and FIG. 10 shows an absorption spectrum of a thin film of BPAPQ.According to FIGS. 9 and 10, it is found that peaks are at 325 nm and402 nm in the case of the toluene solution, and at 328 nm and 418 nm inthe case of the thin film state.

FIG. 11 shows a light emission spectrum and an excitation spectrum ofthe toluene solution of BPAPQ. According to FIG. 11, it is found thatthe light emission maximum is at 483 nm in the toluene solution. FIG. 12shows a light emission spectrum of a thin film (solid state) of BPAPQexcited by ultraviolet rays having a wavelength of 365 nm. According toFIG. 12, the light emission maximum is at 499 nm in the solid state.Therefore, it is found that there is no significant difference in lightemission maximum between the toluene solution and the solid state. Thatis, BPAPQ hardly assembles in the solid state due to a twist form of abiphenyl skeleton, and even in the case of the solid state, a shortwavelength light emission can be obtained similarly to a light emissioncolor in the case of the solution state.

A HOMO level in the thin film state is measured by photoelectronspectroscopy (AC-2, manufactured by Riken Keiki Co., Ltd.) inatmospheric air. The measurement result is −5.31 eV. Further, an opticalenergy gap is obtained from a Tauc plot assuming direct transition byusing the data of the absorption spectrum in FIG. 10. The energy gap is2.66 eV. Therefore, a LUMO level is −2.65 eV.

Further, electrochemical stability of BPAPQ is evaluated by a cyclicvoltammetry (CV). An electrochemical analyzer (ALS model 600A,manufactured by BAS Inc.) is used as a measurement device. As for asolution used in the CV measurement, dehydrated dimethylformamide (DMF)is used as a solvent. Tetraperchlorate-n-butylammonium (n-Bu₄NClO₄), asupporting electrolyte, is dissolved in the solvent so as to have aconcentration of 100 mM. Also, BPAPQ, an object to be measured, isdissolved therein such that the concentration thereof is set to be 1 mM.Further, a platinum electrode (PIE platinum electrode, manufactured byBAS Inc.) is used as a work electrode. A platinum electrode (VC-3 Ptcounter electrode (5 cm), manufactured by BAS Inc.) is used as anauxiliary electrode. An Ag/Ag⁺ electrode (RE 5 nonaqueous referenceelectrode, manufactured by BAS Inc.) is used as a reference electrode.The scanning speed is set to be 0.1 V/sec, and 100 cycle CV measurementsare carried out for both an oxidation reaction and a reduction reaction.

FIG. 13 shows an oxidation reaction characteristic of BPAPQ measured byCV measurement, and FIG. 14 shows a reduction reaction characteristic ofBPAPQ measured by CVmeasurement. It is found that a reversible peak isobtained in both the oxidation reaction and the reduction reaction.Further, even when oxidation or reduction is repeated 100 times, acyclic voltamogram hardly changes. This means that BPAPQ is stable withrespect to oxidation and reduction, that is, electrochemically stable.

Embodiment 2

In this embodiment, a synthesis example of2,3-bis{-4-[N,N-di(4-bipheniryl)amino]phenyl}quinoxaline (hereinafterreferred to as BBAPQ), which is the quinoxaline derivative of theinvention expressed by the following structure formula (39), isspecifically shown.

[Step 1]

A synthesis method of N,N-bis(4-bromophenyl)amine is described. Asynthesis scheme of N,N-bis(4-bromophenyl)amine is shown in (C-1).

An ethyl acetate solution (400 mL) containing 10 g (59 mmol) ofdiphenylamine, to which 22.1 g (124 mmol) of N-bromo succinimide isadded, is stirred for 16 hours at room temperature. After completion ofreaction, the reaction mixture is washed with water and an aqueous phaseis subjected to extraction with ethyl acetate. The extraction solutionis mixed with an organic phase. After the obtained organic phase iswashed with saturated saline, the organic phase is dried with magnesiumsulfate. Then, the mixture is subjected to suction filtration and thefiltrate is condensed. The obtained residue is washed with hexane, ahexane suspension is subjected to suction filtration to collect a solid.Accordingly, 9.5 g (yield: 49%) of N,N-bis(4-bromophenyl)amine isobtained as a white solid.

[Step 2]

A synthesis method of N,N-di(4-biphenyl)amine is described. A synthesisscheme of N,N-di(4-biphenylyl)amine is shown in C-2.

In a nitrogen atmosphere, an ethylene glycol dimethyl ether (20 mL)solution containing 9.5 g (29 mmol) of N,N-bis(4-bromophenyl)amine, 7.9g (65 mmol) of phenyl boronic acid, 0.15 g (0.646 mmol) of palladiumacetate, and 1.4 g (4.5 mmol) of tris(o-thryl)phosphine, to which 95 mLof a potassium carbonate solution (2.0 mol/L) is added, is rectified at90° C. for seven hours. After completion of reaction, the reactionmixture is filtrated, and the obtained solid is recrystallized withchloroform and hexane to obtain 6.7 g (yield: 72%) ofN,N-di(4-biphenylyl)amine which is an object as a white powdered solid.

[Step 3]

A synthesis method of2,3-bis{-4-[N,N-di(4-bipheniryl)amino]phenyl}quinoxaline (hereinafterreferred to as BBAPQ) is described. A synthesis scheme of BBAPQ is shownin (C-3).

In a nitrogen atmosphere, a toluene suspension (80 mL) containing 3.0 g(8.1 mmol) of 2,3-bis(4-bromophenyl)quinoxaline which is synthesized inthe step 1 of Embodiment 1, 5.7 g (18 mmol) ofN,N-di(4-biphenylyl)amine, 0.23 g (0.41 mmol) ofbis(dibenzylidineacetone)palladium(0), and 3.9 g (41 mmol) oftert-butoxy sodium, to which 0.082 g (0.41 mmol) oftri-tert-butylphosphine is added, is heated at 80° C. for eight hours.After completion of reaction, the reaction mixture is subjected tosuction filtration, the obtained solid is dissolved in chloroform, thesolution is subjected to suction filtration through celite, Florisil,and alumina. Then, the filtrate is condensed. The obtained residue isrecrystallized with chloroform and hexane to obtain 5.7 g (yield: 76%)of BBAPQ which is an object, as an yellow solid.

An analysis result of BBAPQ by a proton nuclear magnetic resonancespectroscopy (¹H NMR) is as follows. ¹H NMR (300 MHz, CDCl₃);δ=8.18-8.15 (m, 2H), 7.76-7.73 (m, 2H), and 7.58-7.16 (m, 44H). FIG. 16Ashows an NMR chart of BBAPQ, and FIG. 16B shows an enlarged NMR chart ofa part of 6 to 9 ppm.

A decomposition temperature (Td) of BBAPQ is measured by athermo-gravimetric/differential thermal analyzer (TG/DTA 320,manufactured by Seiko Instruments Inc.). Then, it is found that the Tdis 486° C. and BBAPQ shows preferable heat resistance.

Further, the glass transition point is measured by a differentialscanning calorimeter (DSC, Pyris 1, manufactured by Perkin Elmer Co.,Ltd.). After the sample is heated to 380° C. at 40° C./min to be melted,it is cooled to −10° C. at 40° C./min. After that, the temperature isrisen up to 380° C. at 10° C./min, and thus, a DSC chart shown in FIG.23 is obtained. According to this chart, it is found that the glasstransition point (Tg) of BBAPQ is 140° C. Note that it is known that themelting point is 321° C. from the DSC chart of the case where the sampleis melted first. Therefore, it is found that BBAPQ has a high glasstransition point.

FIG. 17 shows an absorption spectrum of the toluene solution of BBAPQ.According to FIG. 17, it is found that peaks are at 305 nm and 375 nm inthe case of the toluene solution.

Subsequently, electrochemical stability, of BBAPQ is evaluated. Theevaluation method is similar to that of electrochemical stability ofBPAPQ, which is described in Embodiment 1.

FIG. 21 shows an oxidation reaction characteristic of BBAPQ measured byCV measurement, and FIG. 22 shows a reduction reaction characteristic ofBBAPQ measured by CV measurement. It is found that a reversible peak isobtained in both the oxidation reaction and the reduction reaction.Further, even when oxidation or reduction is repeated 100 times, acyclic voltamogram hardly changes. This means that BBAPQ is stable withrespect to oxidation and reduction, that is, electrochemically stable.

Embodiment 3

In this embodiment, the light emitting element of the invention isdescribed with reference to FIG. 37.

Indium tin oxide containing silicon oxide is formed over a glasssubstrate 2101 by sputtering as a first electrode 2102. The filmthickness of the first electrode is 110 nm and the area thereof is 2mm×2 mm.

The substrate provided with the first electrode is fixed on a substrateholder which is provided in a vacuum evaporation apparatus, in such away that a surface provided with the first electrode faces downward.After that, the air inside the vacuum evaporation apparatus is evacuatedto approximately 10⁻⁴ Pa. Then, a layer including a composite material2103 is formed over the first electrode 2102 by co-evaporation of NPBand molybdenum oxide (VI). The film thickness is 50 nm and the weightratio between NPB and molybdenum oxide (VI) is adjusted to be 4:1(=NPB:molybdenum oxide). It is to be noted that the co-evaporation is anevaporation method by which evaporation is carried out simultaneouslyfrom a plurality of evaporation sources each holding a differentmaterial in one process chamber.

Then, a hole transporting layer 2104 is formed over the layer includingthe composite material 2103 to have a thickness of 10 nm using NPB byevaporation with resistive heating.

Further, a light emitting layer 2105 is formed over the holetransporting layer 2104 to have a thickness of 30 nm by co-evaporationof 2,3-bis{4-[N-(4-bipheniryl)-N-phenylamino]phenyl}quinoxaline(hereinafter referred to as BPAPQ) which is the quinoxaline derivativeof the invention expressed by the structure formula (14) and(acetylacetonate)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(hereinafter referred to as Ir(Fdpq)₂(acac)) which is expressed by thestructure formula (114). Here, the weight ratio between BPAPQ andIr(Fdpq)₂(acac) is adjusted to be 1:0.1 (=BPAPQ:Ir(Fdpq)₂(acac)).Consequently, Ir(Fdpq)₂(acac) is dispersed in the layer containingBPAPQ.

After that, an electron transporting layer 2106 is formed over the lightemitting layer 2105 by depositing Alq so as to have a thickness of 10 nmby evaporation with resistive heating.

Further, an electron injecting layer 2107 is formed over the electrontransporting layer 2106 so as to have a thickness of 50 nm byco-evaporation of Alq and lithium. The weight ratio between Alq andlithium is adjusted to be 1:0.01 (=Alq:lithium). Consequently, lithiumis dispersed in a layer containing Alq.

Finally, a second electrode 2108 is formed over the electron injectinglayer 2107 by depositing aluminum so as to have a thickness of 200 nm byevaporation with resistive heating. Thus, the light emitting element ofEmbodiment 3 is formed.

Current density-luminance characteristics of the light emitting elementof Embodiment 3 are shown in FIG. 18. Luminance-voltage characteristicsthereof are shown in FIG. 19. Current efficiency-luminancecharacteristics thereof are shown in FIG. 20. Also, a light emissionspectrum upon applying a current of 1 mA through the light emittingelement is shown in FIG. 33. In the light emitting element of Embodiment3, the voltage required for obtaining a luminance of 970 cd/m² is 6.2 V.The current flowing through the light emitting element in this case is1.40 mA (the current density is 34.9 mA/cm²). The CIE chromaticitycoordinates are (x=0.66, y=0.32). In addition, the current efficiencyand the power efficiency in this case are 2.8 cd/A and 1.41 m/Wrespectively.

As described above, a red light emitting element consuming low power canbe formed by combining the quinoxaline derivative of the invention andthe organometallic complex.

Further, a light emitting element having the same structure as the abovelight emitting element is formed and initial luminance is set to be 1000cd/m². Under such a condition, a continuous lighting test is carried outby constant current driving. Then, it is found that the light emittingelement still holds 82% of the initial luminance even 860 hours later.Therefore, a long-life light emitting element can be obtained by usingthe quinoxaline derivative of the invention.

Embodiment 4

In this embodiment, the light emitting element of the invention isdescribed with reference to FIG. 37.

Indium tin oxide containing silicon oxide is formed over a glasssubstrate 2101 by sputtering as a first electrode 2102. The filmthickness of the first electrode is 110 nm and the area thereof is 2mm×2 mm.

The substrate provided with the first electrode is fixed on a substrateholder which is provided in a vacuum evaporation apparatus, in such away that a surface provided with the first electrode faces downward.After that, the air inside the vacuum evaporation apparatus is evacuatedto approximately 10⁻⁴ Pa. Then, a layer including a composite material2103 is formed over the first electrode 2102 by co-evaporation of NPBand molybdenum oxide (VI). The film thickness is 50 nm and the weightratio between NPB and molybdenum oxide (VI) is adjusted to be 4:1NPB:molybdenum oxide).

Then, a hole transporting layer 2104 is formed over the layer includingthe composite material 2103 so as to have a thickness of 10 nm using NPBby evaporation with resistive heating.

Further, a light emitting layer 2105 is formed over the holetransporting layer 2104 to have a thickness of 30 nm by co-evaporationof 2,3-bis{4-[N,N-di(4-bipheniryl)amino]phenyl}quinoxaline (hereinafterreferred to as BBAPQ) which is the quinoxaline derivative of theinvention expressed by the structure formula (39) and(acetylacetonate)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(hereinafter referred to as Ir(Fdpq)₂(acac)) which is expressed by thestructure formula (114). Here, the weight ratio between BBAPQ andIr(Fdpq)₂(acac) is adjusted to be 1:0.1 (=BBAPQ:Ir(Fdpq)₂(acac)).Consequently, Ir(Fdpq)₂(acac) is dispersed in the layer containingBBAPQ.

After that, an electron transporting layer 2106 is formed over the lightemitting layer 2105 by depositing Alq so as to have a thickness of 10 nmby evaporation with resistive heating.

Further, an electron injecting layer 2107 is formed over the electrontransporting layer 2106 so as to have a thickness of 50 nm byco-evaporation of Alq and lithium. The weight ratio between Alq andlithium is adjusted to be 1:0.01 (=Alq:lithium). Consequently, lithiumis dispersed in a layer containing Alq.

Finally, a second electrode 2108 is formed over the electron injectinglayer 2107 by depositing aluminum so as to have a thickness of 200 nm byevaporation with resistive heating. Thus, the light emitting element ofEmbodiment 4 is formed.

Current density-luminance characteristics of the light emitting elementof Embodiment 4 are shown in FIG. 24. Luminance-voltage characteristicsthereof are shown in FIG. 25. Current efficiency-luminancecharacteristics thereof are shown in FIG. 26. Also, a light emissionspectrum upon applying a current of 1 mA through the light emittingelement is shown in FIG. 34. In the light emitting element of Embodiment4, the voltage required for obtaining a luminance of 900 cd/m² is 6.4 V.The current flowing through the light emitting element in this case is1.39 mA (the current density is 34.8 mA/cm²). The CIE chromaticitycoordinates are (x=0.65, y=0.33). In addition, the current efficiencyand the power efficiency in this case are 2.6 cd/A and 1.31 m/Wrespectively.

As described above, a red light emitting element consuming low power canbe formed by combining the quinoxaline derivative of the invention andthe organometallic complex.

Embodiment 5

In this embodiment, the light emitting element of the invention isdescribed with reference to FIG. 37.

Indium tin oxide containing silicon oxide is formed over a glasssubstrate 2101 by sputtering as a first electrode 2102. The filmthickness of the first electrode is 110 nm and the area thereof is 2mm×2 mm.

The substrate provided with the first electrode is fixed on a substrateholder which is provided in a vacuum evaporation apparatus, in such away that a surface provided with the first electrode faces downward.After that, the air inside the vacuum evaporation apparatus is evacuatedto approximately 10⁻⁴ Pa. Then, a layer including a composite material2103 is formed over the first electrode 2102 by co-evaporation of DNTPDand molybdenum oxide (VI). The film thickness is 50 nm and the weightratio between DNTPD and molybdenum oxide (VI) is adjusted to be 4:2(=DNTPD:molybdenum oxide).

Then, a hole transporting layer 2104 is formed over the layer includingthe composite material 2103 so as to have a thickness of 10 nm using NPBby evaporation with resistive heating.

Further, a light emitting layer 2105 is formed over the holetransporting layer 2104 to have a thickness of 30 nm by co-evaporationof 2,3-bis{4-[N-(4-bipheniryl)-N-phenylamino]phenyl}quinoxaline(hereinafter referred to as BPAPQ) which is the quinoxaline derivativeof the invention expressed by the structure formula (14) and(acetylacetonate)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(hereinafter referred to as Ir(Fdpq)₂(acac)) which is expressed by thestructure formula (114). Here, the weight ratio between BPAPQ andIr(Fdpq)₂(acac) is adjusted to be 1:0.1 (=BPAPQ:Ir(Fdpq)₂(acac)).Consequently, Ir(Fdpq)₂(acac) is dispersed in the layer containingBPAPQ.

After that, an electron transporting layer 2106 is formed over the lightemitting layer 2105 by depositing Alq and BPhen so as to havethicknesses of 10 nm and 50 nm respectively by evaporation withresistive heating.

Further, an electron injecting layer 2107 is formed over the electrontransporting layer 2106 by depositing lithium fluoride so as to have athickness of 1 nm.

Finally, a second electrode 2108 is formed over the electron injectinglayer 2107 by depositing aluminum so as to have a thickness of 200 nm byevaporation with resistive heating. Thus, the light emitting element ofEmbodiment 5 is formed.

Current density-luminance characteristics of the light emitting elementof Embodiment 5 are shown in FIG. 27. Luminance-voltage characteristicsthereof are shown in FIG. 28. Current efficiency-luminancecharacteristics thereof are shown in FIG. 29. Also, a light emissionspectrum upon applying a current of 1 mA through the light emittingelement is shown in FIG. 35. In the light emitting element of Embodiment5, the voltage required for obtaining a luminance of 1100 cd/m² is 6.8V. The current flowing through the light emitting element in this caseis 0.99 mA (the current density is 24.8 mA/cm²). The CIE chromaticitycoordinates are (x=0.68, y=0.31). In addition, the current efficiencyand the power efficiency in this case are 4.5 cd/A and 2.11 m/Wrespectively.

As described above, a red light emitting element consuming low power canbe formed by combining the quinoxaline derivative of the invention andthe organometallic complex.

Embodiment 6

In this embodiment, the light emitting element of the invention isdescribed with reference to FIG. 37.

Indium tin oxide containing silicon oxide is formed over a glasssubstrate 2101 by sputtering as a first electrode 2102. The filmthickness of the first electrode is 110 nm and the area thereof is 2mm×2 mm.

The substrate provided with the first electrode is fixed on a substrateholder which is provided in a vacuum evaporation apparatus, in such away that a surface provided with the first electrode faces downward.After that, the air inside the vacuum evaporation apparatus is evacuatedto approximately 10⁻⁴ Pa. Then, a layer including a composite material2103 is formed over the first electrode 2102 by co-evaporation oft-BuDNA and molybdenum oxide (VI). The film thickness is 50 nm and theweight ratio between the t-BuDNA and the molybdenum oxide (VI) isadjusted to be 4:1 (=t-BuDNA:molybdenum oxide).

Then, a hole transporting layer 2104 is formed over the layer includingthe composite material 2103 so as to have a thickness of 10 nm using NPBby evaporation with resistive heating.

Further, a light emitting layer 2105 is formed over the holetransporting layer 2104 to have a thickness of 30 nm by co-evaporationof 2,3-bis{-4-[N-(4-bipheniryl)-N-phenylamino]phenyl}quinoxaline(hereinafter referred to as BPAPQ) which is the quinoxaline derivativeof the invention expressed by the structure formula (14) and(acetylacetonate)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(hereinafter referred to as Ir(Fdpq)₂(acac)) which is expressed by thestructure formula (114). Here, the weight ratio between BPAPQ andIr(Fdpq)₂(acac) is adjusted to be 1:0.1 (=BPAPQ:Ir(Fdpq)₂(acac)).Consequently, Ir(Fdpq)₂(acac) is dispersed in the layer containingBPAPQ.

After that, an electron transporting layer 2106 is formed over the lightemitting layer 2105 by depositing Alq so as to have a thickness of 10 nmby evaporation with resistive heating.

Further, an electron injecting layer 2107 is formed over the electrontransporting layer 2106 so as to have a thickness of 50 nm byco-evaporation of Alq and lithium. The weight ratio between Alq andlithium is adjusted to be 1:0.01 (=Alq:lithium). Consequently, lithiumis dispersed in the layer containing Alq.

Finally, a second electrode 2108 is formed over the electron injectinglayer 2107 by depositing aluminum so as to have a thickness of 200 nm byevaporation with resistive heating. Thus, the light emitting element ofEmbodiment 6 is formed.

Current density-luminance characteristics of the light emitting elementof Embodiment 6 are shown in FIG. 30. Luminance-voltage characteristicsthereof are shown in FIG. 31. Current efficiency-luminancecharacteristics thereof are shown in FIG. 32. Also, a light emissionspectrum upon applying a current of 1 mA through the light emittingelement is shown in FIG. 36. In the light emitting element of Embodiment6, the voltage required for obtaining a luminance of 1000 cd/m² is 5.4V. The current flowing through the light emitting element in this caseis 1.36 mA (the current density is 33.9 mA/cm²). The CIE chromaticitycoordinates are (x=0.65, y=0.33). In addition, the current efficiencyand the power efficiency in this case are 3.0 cd/A and 1.71 m/Wrespectively.

As described above, a red light emitting element consuming low power canbe formed by combining the quinoxaline derivative of the invention andthe organometallic complex.

Further, initial luminance of the light emitting element of EmbodimentMode 6 is set to be 1000 cd/m². Under such a condition, a continuouslighting test is carried out by constant current driving. Then, it isfound that the light emitting element still holds 70% of the initialluminance even 2500 hours later. Therefore, a long-life light emittingelement can be obtained by using the quinoxaline derivative of theinvention.

Embodiment 7

In this embodiment, the light emitting element of the invention isdescribed with reference to FIG. 37.

Indium tin oxide containing silicon oxide is formed over the glasssubstrate 2101 by sputtering as a first electrode 2102. The filmthickness of the first electrode is 110 nm and the area thereof is 2mm×2 mm.

The substrate provided with the first electrode is fixed on a substrateholder which is provided in a vacuum evaporation apparatus, in such away that a surface provided with the first electrode faces downward.After that, the air inside the vacuum evaporation apparatus is evacuatedto approximately 10⁻⁴ Pa. Then, a layer including a composite material2103 is formed over the first electrode 2102 by co-evaporation of NPBand molybdenum oxide (VI). The film thickness is 50 nm and the weightratio between NPB and molybdenum oxide (VI) is adjusted to be 4:1(=NPB:molybdenum oxide).

Then, a hole transporting layer 2104 is formed over the layer includingthe composite material 2103 so as to have a thickness of 10 nm using NPBby evaporation with resistive heating.

Further, a light emitting layer 2105 is formed over the holetransporting layer 2104 to have a thickness of 30 nm by co-evaporationof 2,3-bis{4-[N-(4-bipheniryl)-N-phenylamino]phenyl}quinoxaline(hereinafter referred to as BPAPQ) which is the quinoxaline derivativeof the invention expressed by the structure formula (14) and(acetylacetonate)bis[2-(4-fluorophenyl)-3-methylquinoxalinato]iridium(III)(hereinafter referred to as Ir(MFpq)₂(acac)) which is expressed by thestructure formula (123). Here, the weight ratio between BPAPQ andIr(MFpq)₂(acac) is adjusted to be 1:0.01 (=BPAPQ:Ir(MFpq)₂(acac)).Consequently, Ir(MFpq)₂(acac) is dispersed in the layer containingBPAPQ.

After that, an electron transporting layer 2106 is formed over the lightemitting layer 2105 by depositing BAlq so as to have a thickness of 10nm by evaporation with resistive heating.

Further, an electron injecting layer 2107 is formed over the electrontransporting layer 2106 so as to have a thickness of 50 nm byco-evaporation of Alq and lithium. Here, the weight ratio between Alqand lithium is adjusted to be 1:0.01 (=Alq:lithium). Consequently,lithium is dispersed in the layer containing Alq.

Finally, a second electrode 2108 is formed over the electron injectinglayer 2107 by depositing aluminum so as to have a thickness of 200 nm byevaporation with resistive heating. Thus, the light emitting element ofEmbodiment 7 is formed.

Current density-luminance characteristics of the light emitting elementof Embodiment 7 are shown in FIG. 38. Luminance-voltage characteristicsthereof are shown in FIG. 39. Current efficiency-luminancecharacteristics thereof are shown in FIG. 40. Also, a light emissionspectrum upon applying a current of 1 mA through the light emittingelement is shown in FIG. 41. In the light emitting element of Embodiment7, the voltage required for obtaining a luminance of 1000 cd/m² is 5.6V. The current flowing through the light emitting element in this caseis 0.43 mA (the current density is 10.8 mA/cm²). The CIE chromaticitycoordinates are (x=0.69, y=031). In addition, the current efficiency andthe power efficiency in this case are 9.1 cd/A and 5.11 m/Wrespectively.

Further, initial luminance of the light emitting element of EmbodimentMode 7 is set to be 1000 cd/m². Under such a condition, a continuouslighting test is carried out by constant current driving. Then, it isfound that the light emitting element still holds 90% of the initialluminance even 310 hours later and has a long life. That is, a long-lifelight emitting element can be obtained by applying the invention.

Further, a red light emitting element consuming low power can beobtained by combining the quinoxaline derivative of the invention andthe organometallic complex.

Further, the light emitting element of this embodiment has high lightemission efficiency. Therefore, the light emitting element whichconsumes low power can be obtained.

This application is based on Japanese Patent Application serial no.2005-264253 filed in Japan Patent Office on 12, Sep. 2005, the entirecontents of which are hereby incorporated by reference.

1-32. (canceled)
 33. A lighting device comprising: a pair of electrodes;and a light emitting layer a quinoxaline derivative between the pair ofelectrodes, wherein the quinoxaline derivative is expressed by a generalformula (1)

wherein each of R¹ to R¹² represents one of a hydrogen atom, a halogenatom, an alkyl group, an alkoxyl group, an acyl group, a dialkyl aminogroup, a diarylamino group, a substituted or unsubstituted vinyl group,a substituted or unsubstituted aryl group, and a substituted orunsubstituted heterocycle group, and wherein Ar¹ represents one of asubstituted or unsubstituted biphenyl group and a substituted orunsubstituted terphenyl group, and Ar² represents one of a substitutedor unsubstituted phenyl group, a substituted or unsubstituted biphenylgroup, a substituted or unsubstituted terphenyl group, and a substitutedor unsubstituted monocyclic heterocycle group.
 34. The lighting deviceaccording to claim 33, wherein the quinoxaline derivative is expressedby a general formula (2)


35. The lighting device according to claim 33, wherein the quinoxalinederivative is expressed by a general formula (3)

wherein A represents a substituent expressed by one of a structureformula (4) and a structure formula (5) and Ar² represents one of asubstituted or unsubstituted phenyl group, a substituted orunsubstituted biphenyl group, a substituted or unsubstituted terphenylgroup, and a substituted or unsubstituted monocyclic heterocycle group.36. The lighting device according to claim 33, wherein the quinoxalinederivative is expressed by a general formula (6)

wherein A represents a substituent expressed by one of a structureformula (7) a structure formula (8) and B represents one of hydrogenatom, a substituent expressed by the structure formula (7), and asubstituent expressed by the structure formula (8).
 37. The lightingdevice according to claim 33, wherein the quinoxaline derivative isexpressed by a general formula (9)

wherein A represents a substituent expressed by one of a structureformula (10) and a structure formula (11) and B represents one of ahydrogen atom, a substituent expressed by the structure formula (10) anda substituent expressed by the structure formula (11).
 38. The lightingdevice according to claim 33, wherein the quinoxaline derivative isexpressed by a general formula (14).


39. The lighting device according to claim 33, wherein the quinoxalinederivative is expressed by a general formula (39).


40. The lighting device according to claim 33, wherein the lightemitting layer further comprises a fluorescent substance.
 41. Thelighting device according to claim 33, wherein the light emitting layerfurther comprises a phosphorescent substance.
 42. The lighting deviceaccording to claim 41, wherein the phosphorescent substance is anorganometallic complex including a structure expressed by a generalformula (101)

wherein R¹ to R⁵ each represent one of hydrogen, a halogen element, anacyl group, an alkyl group, an alkoxyl group, an aryl group, a cyanogroup, and a heterocycle group, wherein Ar represents one of aryl groupand a heterocycle group, and wherein M represents an element whichbelongs to one of Group 9 and Group
 10. 43. The lighting deviceaccording to claim 41, wherein the phosphorescent substance is anorganometallic complex expressed by a general formula (104)

wherein R¹ to R⁵ each represent one of hydrogen, a halogen element, anacyl group, an alkyl group, an alkoxyl group, an aryl group, a cyanogroup, and a heterocycle group, wherein Ar represents one of an arylgroup and a heterocycle group, wherein M represents an element whichbelongs to one of Group 9 and Group 10 and when M is a Group 9 element,n=2 is satisfied, whereas when M is a Group 10 element, n=1 issatisfied, and wherein L represents one of a monoanionic ligand having abeta-diketone structure, a monoanionic bidentate chelate ligand having acarboxyl group, and a monoanionic bidentate chelate ligand having aphenol hydroxyl group.
 44. The lighting device according to claim 41,wherein the phosphorescent substance is an organometallic complexexpressed by a general formula (105)

wherein R¹¹ represents one of alkyl groups having 1 to 4 carbon atoms,wherein R¹² to R¹⁵ each represent one of hydrogen, a halogen element, anacyl group, an alkyl group, an alkoxyl group, an aryl group, a cyanogroup, and a heterocycle group, wherein R¹⁶ to R¹⁹ each represent one ofhydrogen, an acyl group, an alkyl group, an alkoxyl group, an arylgroup, a heterocycle group, and an electron-withdrawing substituent,wherein M represents an element which belongs to one of Group 9 andGroup 10 and when M is a Group 9 element, n=2 is satisfied, whereas whenM is a Group 10 element, n=1 is satisfied, and wherein L represents oneof a monoanionic ligand having a beta-diketone structure, a monoanionicbidentate chelate ligand having a carboxyl group, and a monoanionicbidentate chelate ligand having a phenol hydroxyl group.
 45. Thelighting device according to claim 41, wherein the phosphorescentsubstance is an organometallic complex expressed by a general formula(106)

wherein R²² to R³⁴ each represent one of hydrogen, a halogen element, anacyl group, an alkyl group, an alkoxyl group, an aryl group, a cyanogroup, a heterocycle group, and an electron-withdrawing substituent,wherein M represents an element which belongs to one of Group 9 andGroup 10 and when M is a Group 9 element, n=2 is satisfied, whereas whenM is a Group 10 element, n=1 is satisfied, and wherein L represents oneof a monoanionic ligand having a beta-diketone structure, a monoanionicbidentate chelate ligand having a carboxyl group, and a monoanionicbidentate chelate ligand having a phenol hydroxyl group.
 46. Thelighting device according to claim 41, wherein a light emission spectrumof the phosphorescent substance has a peak at 560 to 700 nm.
 47. Thelighting device according to claim 33, wherein the light emitting layerfurther comprises one of a substance having a hole transportingproperty, a substance having a electron transporting property,4,4′-di(N-carbazolyl)-biphenyl (CBP),2,2′,2″-(1,3,5-benzenetriyl)-tris[1-phenyl-1H-benzimidazole] (TPBI),9,10-di(2-naphthyl)anthracene (DNA), and2-tert-butyl-9,10-di(2-naphthyl)anthracene (t-BuDNA).
 48. The lightingdevice according to claim 47, wherein the substance having the holetransporting property is an aromatic amine compound.
 49. The lightingdevice according to claim 47, wherein the substance having the electrontransporting property is a metal complex or an organic compound.
 50. Thelighting device according to claim 33, wherein R⁹, R¹⁰, and R¹¹ arecombined with R¹⁰, R¹¹, and R¹² respectively.
 51. A lighting devicecomprising: a pair of electrodes; a layer including a composite materialbetween the pair of electrodes; and a light emitting layer comprising aquinoxaline derivative between the layer and one of the pair ofelectrodes, wherein the composite material comprises a first organiccompound and an inorganic compound, wherein the quinoxaline derivativeis expressed by a general formula (1)

wherein each of R¹ to R¹² represents one of a hydrogen atom, a halogenatom, an alkyl group, an alkoxyl group, an acyl group, a dialkyl aminogroup, a diarylamino group, a substituted or unsubstituted vinyl group,a substituted or unsubstituted aryl group, and a substituted orunsubstituted heterocycle group, and wherein Ar¹ represents one of asubstituted or unsubstituted biphenyl group and a substituted orunsubstituted terphenyl group, and Ar² represents one of a substitutedor unsubstituted phenyl group, a substituted or unsubstituted biphenylgroup, a substituted or unsubstituted terphenyl group, and a substitutedor unsubstituted monocyclic heterocycle group.
 52. The lighting deviceaccording to claim 51, wherein the quinoxaline derivative is expressedby a general formula (2)


53. The lighting device according to claim 51, wherein the quinoxalinederivative is expressed by a general formula (3)

wherein A represents a substituent expressed by one of a structureformula (4) and a structure formula (5) and Ar² represents one of asubstituted or unsubstituted phenyl group, a substituted orunsubstituted biphenyl group, a substituted or unsubstituted terphenylgroup, and a substituted or unsubstituted monocyclic heterocycle group.54. The lighting device according to claim 51, wherein the quinoxalinederivative is expressed by a general formula (6)

wherein A represents a substituent expressed by one of a structureformula (7) a structure formula (8) and B represents one of hydrogenatom, a substituent expressed by the structure formula (7), and asubstituent expressed by the structure formula (8).
 55. The lightingdevice according to claim 51, wherein the quinoxaline derivative isexpressed by a general formula (9)

wherein A represents a substituent expressed by one of a structureformula (10) and a structure formula (11) and B represents one of ahydrogen atom, a substituent expressed by the structure formula (10) anda substituent expressed by the structure formula (11).
 56. The lightingdevice according to claim 51, wherein the quinoxaline derivative isexpressed by a general formula (14).


57. The lighting device according to claim 51, wherein the quinoxalinederivative is expressed by a general formula (39).


58. The lighting device according to claim 51, wherein the lightemitting layer further comprises a fluorescent substance.
 59. Thelighting device according to claim 51, wherein the light emitting layerfurther comprises a phosphorescent substance.
 60. The lighting deviceaccording to claim 59, wherein the phosphorescent substance is anorganometallic complex including a structure expressed by a generalformula (101)

wherein R¹ to R⁵ each represent one of hydrogen, a halogen element, anacyl group, an alkyl group, an alkoxyl group, an aryl group, a cyanogroup, and a heterocycle group, wherein Ar represents one of aryl groupand a heterocycle group, and wherein M represents an element whichbelongs to one of Group 9 and Group
 10. 61. The lighting deviceaccording to claim 59, wherein the phosphorescent substance is anorganometallic complex expressed by a general formula (104)

wherein R¹ to R⁵ each represent one of hydrogen, a halogen element, anacyl group, an alkyl group, an alkoxyl group, an aryl group, a cyanogroup, and a heterocycle group, wherein Ar represents one of an arylgroup and a heterocycle group, wherein M represents an element whichbelongs to one of Group 9 and Group 10 and when M is a Group 9 element,n=2 is satisfied, whereas when M is a Group 10 element, n=1 issatisfied, and wherein L represents one of a monoanionic ligand having abeta-diketone structure, a monoanionic bidentate chelate ligand having acarboxyl group, and a monoanionic bidentate chelate ligand having aphenol hydroxyl group.
 62. The lighting device according to claim 59,wherein the phosphorescent substance is an organometallic complexexpressed by a general formula (105)

wherein R^(H) represents one of alkyl groups having 1 to 4 carbon atoms,wherein R¹² to R¹⁵ each represent one of hydrogen, a halogen element, anacyl group, an alkyl group, an alkoxyl group, an aryl group, a cyanogroup, and a heterocycle group, wherein R¹⁶ to R¹⁹ each represent one ofhydrogen, an acyl group, an alkyl group, an alkoxyl group, an arylgroup, a heterocycle group, and an electron-withdrawing substituent,wherein M represents an element which belongs to one of Group 9 andGroup 10 and when M is a Group 9 element, n=2 is satisfied, whereas whenM is a Group 10 element, n=1 is satisfied, and wherein L represents oneof a monoanionic ligand having a beta-diketone structure, a monoanionicbidentate chelate ligand having a carboxyl group, and a monoanionicbidentate chelate ligand having a phenol hydroxyl group.
 63. Thelighting device according to claim 59, wherein the phosphorescentsubstance is an organometallic complex expressed by a general formula(106)

wherein R²² to R³⁴ each represent one of hydrogen, a halogen element, anacyl group, an alkyl group, an alkoxyl group, an aryl group, a cyanogroup, a heterocycle group, and an electron-withdrawing substituent,wherein M represents an element which belongs to one of Group 9 andGroup 10 and when M is a Group 9 element, n=2 is satisfied, whereas whenM is a Group 10 element, n=1 is satisfied, and wherein L represents oneof a monoanionic ligand having a beta-diketone structure, a monoanionicbidentate chelate ligand having a carboxyl group, and a monoanionicbidentate chelate ligand having a phenol hydroxyl group.
 64. Thelighting device according to claim 59, wherein a light emission spectrumof the phosphorescent substance has a peak at 560 to 700 nm.
 65. Thelighting device according to claim 51, wherein the light emitting layerfurther comprises one of a substance having a hole transportingproperty, a substance having a electron transporting property,4,4′-di(N-carbazolyl)-biphenyl (CBP),2,2′,2″-(1,3,5-benzenetriyl)-tris[1-phenyl-1H-benzimidazole] (TPBI),9,10-di(2-naphthyl)anthracene (DNA), and2-tert-butyl-9,10-di(2-naphthyl)anthracene (t-BuDNA).
 66. The lightingdevice according to claim 65, wherein the substance having the holetransporting property is an aromatic amine compound.
 67. The lightingdevice according to claim 65, wherein the substance having the electrontransporting property is a metal complex or a second organic compound.68. The lighting device according to claim 51, wherein R⁹, R¹⁰, and R¹¹are combined with R¹⁰, R¹¹, and R¹² respectively.
 69. The lightingdevice according to claim 51, wherein the first organic compound isselected from an aromatic amine-based organic compound, acarbazole-based organic compound and an aromatic hydrocarbon.
 70. Thelighting device according to claim 51, wherein the inorganic compound isa substance showing an electron accepting property with respect to theorganic compound.
 71. The lighting device according to claim 51, whereinthe inorganic compound is an oxide of a transition metal.
 72. Thelighting device according to claim 51, wherein the inorganic compound isselected from titanium oxide, vanadium oxide, molybdenum oxide, tungstenoxide, rhenium oxide, ruthenium oxide, chromium oxide, zirconium oxide,hafnium oxide, tantalum oxide, silver oxide, or manganese oxide.